| PERLFAQ4(1) | Perl Programmers Reference Guide | PERLFAQ4(1) |
Internally, your computer represents floating-point numbers in binary. Digital (as in powers of two) computers cannot store all numbers exactly. Some real numbers lose precision in the process. This is a problem with how computers store numbers and affects all computer languages, not just Perl.
perlnumber shows the gory details of number representations and conversions.
To limit the number of decimal places in your numbers, you can use the "printf" or "sprintf" function. See "Floating-point Arithmetic" in perlop for more details.
printf "%.2f", 10/3; my $number = sprintf "%.2f", 10/3;
First, see the answer to "Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?".
For example, this
print int(0.6/0.2-2), "\n";
will in most computers print 0, not 1, because even such simple numbers as 0.6 and 0.2 cannot be presented exactly by floating-point numbers. What you think in the above as 'three' is really more like 2.9999999999999995559.
You're probably trying to convert a string to a number, which Perl only converts as a decimal number. When Perl converts a string to a number, it ignores leading spaces and zeroes, then assumes the rest of the digits are in base 10:
my $string = '0644'; print $string + 0; # prints 644 print $string + 44; # prints 688, certainly not octal!
This problem usually involves one of the Perl built-ins that has the same name a Unix command that uses octal numbers as arguments on the command line. In this example, "chmod" on the command line knows that its first argument is octal because that's what it does:
%prompt> chmod 644 file
If you want to use the same literal digits (644) in Perl, you have to tell Perl to treat them as octal numbers either by prefixing the digits with a 0 or using "oct":
chmod( 0644, $filename ); # right, has leading zero chmod( oct(644), $filename ); # also correct
The problem comes in when you take your numbers from something that Perl thinks is a string, such as a command line argument in @ARGV:
chmod( $ARGV[0], $filename ); # wrong, even if "0644" chmod( oct($ARGV[0]), $filename ); # correct, treat string as octal
You can always check the value you're using by printing it in octal notation to ensure it matches what you think it should be. Print it in octal and decimal format:
printf "0%o %d", $number, $number;
printf("%.3f", 3.1415926535); # prints 3.142
The POSIX module (part of the standard Perl distribution) implements "ceil()", "floor()", and a number of other mathematical and trigonometric functions.
use POSIX; my $ceil = ceil(3.5); # 4 my $floor = floor(3.5); # 3
In 5.000 to 5.003 perls, trigonometry was done in the Math::Complex module. With 5.004, the Math::Trig module (part of the standard Perl distribution) implements the trigonometric functions. Internally it uses the Math::Complex module and some functions can break out from the real axis into the complex plane, for example the inverse sine of 2.
Rounding in financial applications can have serious implications, and the rounding method used should be specified precisely. In these cases, it probably pays not to trust whichever system of rounding is being used by Perl, but instead to implement the rounding function you need yourself.
To see why, notice how you'll still have an issue on half-way-point alternation:
for (my $i = -5; $i <= 5; $i += 0.5) { printf "%.0f ",$i } -5 -4 -4 -4 -3 -2 -2 -2 -1 -0 0 0 1 2 2 2 3 4 4 4 5
Don't blame Perl. It's the same as in C. IEEE says we have to do this. Perl numbers whose absolute values are integers under 2**31 (on 32-bit machines) will work pretty much like mathematical integers. Other numbers are not guaranteed.
Some of the examples later in perlfaq4 use the Bit::Vector module from CPAN. The reason you might choose Bit::Vector over the perl built-in functions is that it works with numbers of ANY size, that it is optimized for speed on some operations, and for at least some programmers the notation might be familiar.
my $dec = 0xDEADBEEF;
Using the "hex" function:
my $dec = hex("DEADBEEF");
Using "pack":
my $dec = unpack("N", pack("H8", substr("0" x 8 . "DEADBEEF", -8)));
Using the CPAN module "Bit::Vector":
use Bit::Vector; my $vec = Bit::Vector->new_Hex(32, "DEADBEEF"); my $dec = $vec->to_Dec();
my $hex = sprintf("%X",<PHONE_NUMBER>); # upper case A-F my $hex = sprintf("%x",<PHONE_NUMBER>); # lower case a-f
Using "unpack":
my $hex = unpack("H*", pack("N",<PHONE_NUMBER>));
Using Bit::Vector:
use Bit::Vector; my $vec = Bit::Vector->new_Dec(32, -559038737); my $hex = $vec->to_Hex();
And Bit::Vector supports odd bit counts:
use Bit::Vector; my $vec = Bit::Vector->new_Dec(33,<PHONE_NUMBER>); $vec->Resize(32); # suppress leading 0 if unwanted my $hex = $vec->to_Hex();
my $dec =<PHONE_NUMBER>57; # note the leading 0!
Using the "oct" function:
my $dec = oct("33653337357");
Using Bit::Vector:
use Bit::Vector; my $vec = Bit::Vector->new(32); $vec->Chunk_List_Store(3, split(//, reverse "33653337357")); my $dec = $vec->to_Dec();
my $oct = sprintf("%o",<PHONE_NUMBER>);
Using Bit::Vector:
use Bit::Vector; my $vec = Bit::Vector->new_Dec(32, -559038737); my $oct = reverse join('', $vec->Chunk_List_Read(3));
my $number = 0b10110110;
Using "oct":
my $input = "10110110"; my $decimal = oct( "0b$input" );
Using "pack" and "ord":
my $decimal = ord(pack('B8', '10110110'));
Using "pack" and "unpack" for larger strings:
my $int = unpack("N", pack("B32", substr("0" x 32 . "11110101011011011111011101111", -32))); my $dec = sprintf("%d", $int); # substr() is used to left-pad a 32-character string with zeros.
Using Bit::Vector:
my $vec = Bit::Vector->new_Bin(32, "11011110101011011011111011101111"); my $dec = $vec->to_Dec();
my $bin = sprintf("%b",<PHONE_NUMBER>);
Using "unpack":
my $bin = unpack("B*", pack("N",<PHONE_NUMBER>));
Using Bit::Vector:
use Bit::Vector; my $vec = Bit::Vector->new_Dec(32, -559038737); my $bin = $vec->to_Bin();
The remaining transformations (e.g. hex -> oct, bin -> hex, etc.) are left as an exercise to the inclined reader.
So, saying "11 & 3" performs the "and" operation on numbers (yielding 3). Saying "11" & "3" performs the "and" operation on strings (yielding "1").
Most problems with "&" and "|" arise because the programmer thinks they have a number but really it's a string or vice versa. To avoid this, stringify the arguments explicitly (using "" or "qq()") or convert them to numbers explicitly (using "0+$arg"). The rest arise because the programmer says:
if ("\020\020" & "\101\101") { # ... }
but a string consisting of two null bytes (the result of "\020\020" & "\101\101") is not a false value in Perl. You need:
if ( ("\020\020" & "\101\101") !~ /[^\000]/) { # ... }
my @results = map { my_func($_) } @array;
For example:
my @triple = map { 3 * $_ } @single;
To call a function on each element of an array, but ignore the results:
foreach my $iterator (@array) { some_func($iterator); }
To call a function on each integer in a (small) range, you can use:
my @results = map { some_func($_) } (5 .. 25);
but you should be aware that in this form, the ".." operator creates a list of all integers in the range, which can take a lot of memory for large ranges. However, the problem does not occur when using ".." within a "for" loop, because in that case the range operator is optimized to iterate over the range, without creating the entire list. So
my @results = (); for my $i (5 .. 500_005) { push(@results, some_func($i)); }
or even
push(@results, some_func($_)) for 5 .. 500_005;
will not create an intermediate list of 500,000 integers.
BEGIN { srand() if $] < 5.004 }
5.004 and later automatically call "srand" at the beginning. Don't call "srand" more than once--you make your numbers less random, rather than more.
Computers are good at being predictable and bad at being random (despite appearances caused by bugs in your programs :-). The random article in the "Far More Than You Ever Wanted To Know" collection in <http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz>, courtesy of Tom Phoenix, talks more about this. John von Neumann said, "Anyone who attempts to generate random numbers by deterministic means is, of course, living in a state of sin."
Perl relies on the underlying system for the implementation of "rand" and "srand"; on some systems, the generated numbers are not random enough (especially on Windows : see <http://www.perlmonks.org/?node_id=803632>). Several CPAN modules in the "Math" namespace implement better pseudorandom generators; see for example Math::Random::MT ("Mersenne Twister", fast), or Math::TrulyRandom (uses the imperfections in the system's timer to generate random numbers, which is rather slow). More algorithms for random numbers are described in "Numerical Recipes in C" at <http://www.nr.com/>
"rand($x)" returns a number such that "0 <= rand($x) < $x". Thus what you want to have perl figure out is a random number in the range from 0 to the difference between your X and Y.
That is, to get a number between 10 and 15, inclusive, you want a random number between 0 and 5 that you can then add to 10.
my $number = 10 + int rand( 15-10+1 ); # ( 10,11,12,13,14, or 15 )
Hence you derive the following simple function to abstract that. It selects a random integer between the two given integers (inclusive). For example: "random_int_between(50,120)".
sub random_int_between { my($min, $max) = @_; # Assumes that the two arguments are integers themselves! return $min if $min == $max; ($min, $max) = ($max, $min) if $min > $max; return $min + int rand(1 + $max - $min); }
my $day_of_year = (localtime)[7];
The POSIX module can also format a date as the day of the year or week of the year.
use POSIX qw/strftime/; my $day_of_year = strftime "%j", localtime; my $week_of_year = strftime "%W", localtime;
To get the day of year for any date, use POSIX's "mktime" to get a time in epoch seconds for the argument to "localtime".
use POSIX qw/mktime strftime/; my $week_of_year = strftime "%W", localtime( mktime( 0, 0, 0, 18, 11, 87 ) );
You can also use Time::Piece, which comes with Perl and provides a "localtime" that returns an object:
use Time::Piece; my $day_of_year = localtime->yday; my $week_of_year = localtime->week;
The Date::Calc module provides two functions to calculate these, too:
use Date::Calc; my $day_of_year = Day_of_Year( 1987, 12, 18 ); my $week_of_year = Week_of_Year( 1987, 12, 18 );
sub get_century { return int((((localtime(shift || time))[5] + 1999))/100); } sub get_millennium { return 1+int((((localtime(shift || time))[5] + 1899))/1000); }
On some systems, the POSIX module's "strftime()" function has been extended in a non-standard way to use a %C format, which they sometimes claim is the "century". It isn't, because on most such systems, this is only the first two digits of the four-digit year, and thus cannot be used to determine reliably the current century or millennium.
You could just store all your dates as a number and then subtract. Life isn't always that simple though.
The Time::Piece module, which comes with Perl, replaces localtime with a version that returns an object. It also overloads the comparison operators so you can compare them directly:
use Time::Piece; my $date1 = localtime( $some_time ); my $date2 = localtime( $some_other_time ); if( $date1 < $date2 ) { print "The date was in the past\n"; }
You can also get differences with a subtraction, which returns a Time::Seconds object:
my $date_diff = $date1 - $date2; print "The difference is ", $date_diff->days, " days\n";
If you want to work with formatted dates, the Date::Manip, Date::Calc, or DateTime modules can help you.
You can use the Time::Piece module, part of the Standard Library, which can convert a date/time to a Julian Day:
$ perl -MTime::Piece -le 'print localtime->julian_day' 2455607.7959375
Or the modified Julian Day:
$ perl -MTime::Piece -le 'print localtime->mjd' 55607.2961226851
Or even the day of the year (which is what some people think of as a Julian day):
$ perl -MTime::Piece -le 'print localtime->yday' 45
You can also do the same things with the DateTime module:
$ perl -MDateTime -le'print DateTime->today->jd' 2453401.5 $ perl -MDateTime -le'print DateTime->today->mjd' 53401 $ perl -MDateTime -le'print DateTime->today->doy' 31
You can use the Time::JulianDay module available on CPAN. Ensure that you really want to find a Julian day, though, as many people have different ideas about Julian days (see <http://www.hermetic.ch/cal_stud/jdn.htm> for instance):
$ perl -MTime::JulianDay -le 'print local_julian_day( time )' 55608
To do it correctly, you can use one of the "Date" modules since they work with calendars instead of times. The DateTime module makes it simple, and give you the same time of day, only the day before, despite daylight saving time changes:
use DateTime; my $yesterday = DateTime->now->subtract( days => 1 ); print "Yesterday was $yesterday\n";
You can also use the Date::Calc module using its "Today_and_Now" function.
use Date::Calc qw( Today_and_Now Add_Delta_DHMS ); my @date_time = Add_Delta_DHMS( Today_and_Now(), -1, 0, 0, 0 ); print "@date_time\n";
Most people try to use the time rather than the calendar to figure out dates, but that assumes that days are twenty-four hours each. For most people, there are two days a year when they aren't: the switch to and from summer time throws this off. For example, the rest of the suggestions will be wrong sometimes:
Starting with Perl 5.10, Time::Piece and Time::Seconds are part of the standard distribution, so you might think that you could do something like this:
use Time::Piece; use Time::Seconds; my $yesterday = localtime() - ONE_DAY; # WRONG print "Yesterday was $yesterday\n";
The Time::Piece module exports a new "localtime" that returns an object, and Time::Seconds exports the "ONE_DAY" constant that is a set number of seconds. This means that it always gives the time 24 hours ago, which is not always yesterday. This can cause problems around the end of daylight saving time when there's one day that is 25 hours long.
You have the same problem with Time::Local, which will give the wrong answer for those same special cases:
# contributed by Gunnar Hjalmarsson use Time::Local; my $today = timelocal 0, 0, 12, ( localtime )[3..5]; my ($d, $m, $y) = ( localtime $today-86400 )[3..5]; # WRONG printf "Yesterday: %d-%02d-%02d\n", $y+1900, $m+1, $d;
Perl itself never had a Y2K problem, although that never stopped people from creating Y2K problems on their own. See the documentation for "localtime" for its proper use.
Starting with Perl 5.12, "localtime" and "gmtime" can handle dates past 03:14:08 January 19, 2038, when a 32-bit based time would overflow. You still might get a warning on a 32-bit "perl":
% perl5.12 -E 'say scalar localtime( 0x9FFF_FFFFFFFF )' Integer overflow in hexadecimal number at -e line 1. Wed Nov 1 19:42:39 5576711
On a 64-bit "perl", you can get even larger dates for those really long running projects:
% perl5.12 -E 'say scalar gmtime( 0x9FFF_FFFFFFFF )' Thu Nov 2 00:42:39 5576711
You're still out of luck if you need to keep track of decaying protons though.
There are many ways to ensure that values are what you expect or want to accept. Besides the specific examples that we cover in the perlfaq, you can also look at the modules with "Assert" and "Validate" in their names, along with other modules such as Regexp::Common.
Some modules have validation for particular types of input, such as Business::ISBN, Business::CreditCard, Email::Valid, and Data::Validate::IP.
s/\\(.)/$1/g;
This won't expand "\n" or "\t" or any other special escapes.
You can use the substitution operator to find pairs of characters (or runs of characters) and replace them with a single instance. In this substitution, we find a character in "(.)". The memory parentheses store the matched character in the back-reference "\g1" and we use that to require that the same thing immediately follow it. We replace that part of the string with the character in $1.
s/(.)\g1/$1/g;
We can also use the transliteration operator, "tr///". In this example, the search list side of our "tr///" contains nothing, but the "c" option complements that so it contains everything. The replacement list also contains nothing, so the transliteration is almost a no-op since it won't do any replacements (or more exactly, replace the character with itself). However, the "s" option squashes duplicated and consecutive characters in the string so a character does not show up next to itself
my $str = 'Haarlem'; # in the Netherlands $str =~ tr///cs; # Now Harlem, like in New York
This is documented in perlref, and although it's not the easiest thing to read, it does work. In each of these examples, we call the function inside the braces used to dereference a reference. If we have more than one return value, we can construct and dereference an anonymous array. In this case, we call the function in list context.
print "The time values are @{ [localtime] }.\n";
If we want to call the function in scalar context, we have to do a bit more work. We can really have any code we like inside the braces, so we simply have to end with the scalar reference, although how you do that is up to you, and you can use code inside the braces. Note that the use of parens creates a list context, so we need "scalar" to force the scalar context on the function:
print "The time is ${\(scalar localtime)}.\n" print "The time is ${ my $x = localtime; \$x }.\n";
If your function already returns a reference, you don't need to create the reference yourself.
sub timestamp { my $t = localtime; \$t } print "The time is ${ timestamp() }.\n";
The "Interpolation" module can also do a lot of magic for you. You can specify a variable name, in this case "E", to set up a tied hash that does the interpolation for you. It has several other methods to do this as well.
use Interpolation E => 'eval'; print "The time values are $E{localtime()}.\n";
In most cases, it is probably easier to simply use string concatenation, which also forces scalar context.
print "The time is " . localtime() . ".\n";
More complex cases will require to write a parser, probably using a parsing module from CPAN, like Regexp::Grammars, Parse::RecDescent, Parse::Yapp, Text::Balanced, or Marpa::R2.
my $reversed = reverse $string;
1 while $string =~ s/\t+/' ' x (length($&) * 8 - length($`) % 8)/e;
Or you can just use the Text::Tabs module (part of the standard Perl distribution).
use Text::Tabs; my @expanded_lines = expand(@lines_with_tabs);
use Text::Wrap; print wrap("\t", ' ', @paragraphs);
The paragraphs you give to Text::Wrap should not contain embedded newlines. Text::Wrap doesn't justify the lines (flush-right).
Or use the CPAN module Text::Autoformat. Formatting files can be easily done by making a shell alias, like so:
alias fmt="perl -i -MText::Autoformat -n0777 \ -e 'print autoformat $_, {all=>1}' $*"
See the documentation for Text::Autoformat to appreciate its many capabilities.
my $string = "Just another Perl Hacker"; my $first_char = substr( $string, 0, 1 ); # 'J'
To change part of a string, you can use the optional fourth argument which is the replacement string.
substr( $string, 13, 4, "Perl 5.8.0" );
You can also use substr() as an lvalue.
substr( $string, 13, 4 ) = "Perl 5.8.0";
$count = 0; s{((whom?)ever)}{ ++$count == 5 # is it the 5th? ? "${2}soever" # yes, swap : $1 # renege and leave it there }ige;
In the more general case, you can use the "/g" modifier in a "while" loop, keeping count of matches.
$WANT = 3; $count = 0; $_ = "One fish two fish red fish blue fish"; while (/(\w+)\s+fish\b/gi) { if (++$count == $WANT) { print "The third fish is a $1 one.\n"; } }
That prints out: "The third fish is a red one." You can also use a repetition count and repeated pattern like this:
/(?:\w+\s+fish\s+){2}(\w+)\s+fish/i;
my $string = "ThisXlineXhasXsomeXx'sXinXit"; my $count = ($string =~ tr/X//); print "There are $count X characters in the string";
This is fine if you are just looking for a single character. However, if you are trying to count multiple character substrings within a larger string, "tr///" won't work. What you can do is wrap a while() loop around a global pattern match. For example, let's count negative integers:
my $string = "-9 55 48 -2 23 -76 4 14 -44"; my $count = 0; while ($string =~ /-\d+/g) { $count++ } print "There are $count negative numbers in the string";
Another version uses a global match in list context, then assigns the result to a scalar, producing a count of the number of matches.
my $count = () = $string =~ /-\d+/g;
Damian Conway's Text::Autoformat handles all of the thinking for you.
use Text::Autoformat; my $x = "Dr. Strangelove or: How I Learned to Stop ". "Worrying and Love the Bomb"; print $x, "\n"; for my $style (qw( sentence title highlight )) { print autoformat($x, { case => $style }), "\n"; }
How do you want to capitalize those words?
FRED AND BARNEY'S LODGE # all uppercase Fred And Barney's Lodge # title case Fred and Barney's Lodge # highlight case
It's not as easy a problem as it looks. How many words do you think are in there? Wait for it... wait for it.... If you answered 5 you're right. Perl words are groups of "\w+", but that's not what you want to capitalize. How is Perl supposed to know not to capitalize that "s" after the apostrophe? You could try a regular expression:
$string =~ s/ ( (^\w) #at the beginning of the line | # or (\s\w) #preceded by whitespace ) /\U$1/xg; $string =~ s/([\w']+)/\u\L$1/g;
Now, what if you don't want to capitalize that "and"? Just use Text::Autoformat and get on with the next problem. :)
Take the example case of trying to split a string that is comma-separated into its different fields. You can't use "split(/,/)" because you shouldn't split if the comma is inside quotes. For example, take a data line like this:
SAR001,"","Cimetrix, Inc","Bob Smith","CAM",N,8,1,0,7,"Error, Core Dumped"
Due to the restriction of the quotes, this is a fairly complex problem. Thankfully, we have Jeffrey Friedl, author of Mastering Regular Expressions, to handle these for us. He suggests (assuming your string is contained in $text):
my @new = (); push(@new, $+) while $text =~ m{ "([^\"\\]*(?:\\.[^\"\\]*)*)",? # groups the phrase inside the quotes | ([^,]+),? | , }gx; push(@new, undef) if substr($text,-1,1) eq ',';
If you want to represent quotation marks inside a quotation-mark-delimited field, escape them with backslashes (eg, "like \"this\"".
Alternatively, the Text::ParseWords module (part of the standard Perl distribution) lets you say:
use Text::ParseWords; @new = quotewords(",", 0, $text);
For parsing or generating CSV, though, using Text::CSV rather than implementing it yourself is highly recommended; you'll save yourself odd bugs popping up later by just using code which has already been tried and tested in production for years.
A substitution can do this for you. For a single line, you want to replace all the leading or trailing whitespace with nothing. You can do that with a pair of substitutions:
s/^\s+//; s/\s+$//;
You can also write that as a single substitution, although it turns out the combined statement is slower than the separate ones. That might not matter to you, though:
s/^\s+|\s+$//g;
In this regular expression, the alternation matches either at the beginning or the end of the string since the anchors have a lower precedence than the alternation. With the "/g" flag, the substitution makes all possible matches, so it gets both. Remember, the trailing newline matches the "\s+", and the "$" anchor can match to the absolute end of the string, so the newline disappears too. Just add the newline to the output, which has the added benefit of preserving "blank" (consisting entirely of whitespace) lines which the "^\s+" would remove all by itself:
while( <> ) { s/^\s+|\s+$//g; print "$_\n"; }
For a multi-line string, you can apply the regular expression to each logical line in the string by adding the "/m" flag (for "multi-line"). With the "/m" flag, the "$" matches before an embedded newline, so it doesn't remove it. This pattern still removes the newline at the end of the string:
$string =~ s/^\s+|\s+$//gm;
Remember that lines consisting entirely of whitespace will disappear, since the first part of the alternation can match the entire string and replace it with nothing. If you need to keep embedded blank lines, you have to do a little more work. Instead of matching any whitespace (since that includes a newline), just match the other whitespace:
$string =~ s/^[\t\f ]+|[\t\f ]+$//mg;
The simplest method uses the "sprintf" function. It can pad on the left or right with blanks and on the left with zeroes and it will not truncate the result. The "pack" function can only pad strings on the right with blanks and it will truncate the result to a maximum length of $pad_len.
# Left padding a string with blanks (no truncation): my $padded = sprintf("%${pad_len}s", $text); my $padded = sprintf("%*s", $pad_len, $text); # same thing # Right padding a string with blanks (no truncation): my $padded = sprintf("%-${pad_len}s", $text); my $padded = sprintf("%-*s", $pad_len, $text); # same thing # Left padding a number with 0 (no truncation): my $padded = sprintf("%0${pad_len}d", $num); my $padded = sprintf("%0*d", $pad_len, $num); # same thing # Right padding a string with blanks using pack (will truncate): my $padded = pack("A$pad_len",$text);
If you need to pad with a character other than blank or zero you can use one of the following methods. They all generate a pad string with the "x" operator and combine that with $text. These methods do not truncate $text.
Left and right padding with any character, creating a new string:
my $padded = $pad_char x ( $pad_len - length( $text ) ) . $text; my $padded = $text . $pad_char x ( $pad_len - length( $text ) );
Left and right padding with any character, modifying $text directly:
substr( $text, 0, 0 ) = $pad_char x ( $pad_len - length( $text ) ); $text .= $pad_char x ( $pad_len - length( $text ) );
If you know the columns that contain the data, you can use "substr" to extract a single column.
my $column = substr( $line, $start_column, $length );
You can use "split" if the columns are separated by whitespace or some other delimiter, as long as whitespace or the delimiter cannot appear as part of the data.
my $line = ' fred barney betty '; my @columns = split /\s+/, $line; # ( '', 'fred', 'barney', 'betty' ); my $line = 'fred||barney||betty'; my @columns = split /\|/, $line; # ( 'fred', '', 'barney', '', 'betty' );
If you want to work with comma-separated values, don't do this since that format is a bit more complicated. Use one of the modules that handle that format, such as Text::CSV, Text::CSV_XS, or Text::CSV_PP.
If you want to break apart an entire line of fixed columns, you can use "unpack" with the A (ASCII) format. By using a number after the format specifier, you can denote the column width. See the "pack" and "unpack" entries in perlfunc for more details.
my @fields = unpack( $line, "A8 A8 A8 A16 A4" );
Note that spaces in the format argument to "unpack" do not denote literal spaces. If you have space separated data, you may want "split" instead.
You can use the "Text::Soundex" module. If you want to do fuzzy or close matching, you might also try the String::Approx, and Text::Metaphone, and Text::DoubleMetaphone modules.
If you can avoid it, don't, or if you can use a templating system, such as Text::Template or Template Toolkit, do that instead. You might even be able to get the job done with "sprintf" or "printf":
my $string = sprintf 'Say hello to %s and %s', $foo, $bar;
However, for the one-off simple case where I don't want to pull out a full templating system, I'll use a string that has two Perl scalar variables in it. In this example, I want to expand $foo and $bar to their variable's values:
my $foo = 'Fred'; my $bar = 'Barney'; $string = 'Say hello to $foo and $bar';
One way I can do this involves the substitution operator and a double "/e" flag. The first "/e" evaluates $1 on the replacement side and turns it into $foo. The second /e starts with $foo and replaces it with its value. $foo, then, turns into 'Fred', and that's finally what's left in the string:
$string =~ s/(\$\w+)/$1/eeg; # 'Say hello to Fred and Barney'
The "/e" will also silently ignore violations of strict, replacing undefined variable names with the empty string. Since I'm using the "/e" flag (twice even!), I have all of the same security problems I have with "eval" in its string form. If there's something odd in $foo, perhaps something like "@{[ system "rm -rf /" ]}", then I could get myself in trouble.
To get around the security problem, I could also pull the values from a hash instead of evaluating variable names. Using a single "/e", I can check the hash to ensure the value exists, and if it doesn't, I can replace the missing value with a marker, in this case "???" to signal that I missed something:
my $string = 'This has $foo and $bar'; my %Replacements = ( foo => 'Fred', ); # $string =~ s/\$(\w+)/$Replacements{$1}/g; $string =~ s/\$(\w+)/ exists $Replacements{$1} ? $Replacements{$1} : '???' /eg; print $string;
If you get used to writing odd things like these:
print "$var"; # BAD my $new = "$old"; # BAD somefunc("$var"); # BAD
You'll be in trouble. Those should (in 99.8% of the cases) be the simpler and more direct:
print $var; my $new = $old; somefunc($var);
Otherwise, besides slowing you down, you're going to break code when the thing in the scalar is actually neither a string nor a number, but a reference:
func(\@array); sub func { my $aref = shift; my $oref = "$aref"; # WRONG }
You can also get into subtle problems on those few operations in Perl that actually do care about the difference between a string and a number, such as the magical "++" autoincrement operator or the syscall() function.
Stringification also destroys arrays.
my @lines = `command`; print "@lines"; # WRONG - extra blanks print @lines; # right
If you want to indent the text in the here document, you can do this:
# all in one (my $VAR = <<HERE_TARGET) =~ s/^\s+//gm; your text goes here HERE_TARGET
But the HERE_TARGET must still be flush against the margin. If you want that indented also, you'll have to quote in the indentation.
(my $quote = <<' FINIS') =~ s/^\s+//gm; ...we will have peace, when you and all your works have perished--and the works of your dark master to whom you would deliver us.  --Theoden in /usr/src/perl/taint.c FINIS $quote =~ s/\s+--/\n--/;
A nice general-purpose fixer-upper function for indented here documents follows. It expects to be called with a here document as its argument. It looks to see whether each line begins with a common substring, and if so, strips that substring off. Otherwise, it takes the amount of leading whitespace found on the first line and removes that much off each subsequent line.
sub fix { local $_ = shift; my ($white, $leader); # common whitespace and common leading string if (/^\s*(?:([^\w\s]+)(\s*).*\n)(?:\s*\g1\g2?.*\n)+$/) { ($white, $leader) = ($2, quotemeta($1)); } else { ($white, $leader) = (/^(\s+)/, ''); } s/^\s*?$leader(?:$white)?//gm; return $_; }
This works with leading special strings, dynamically determined:
my $remember_the_main = fix<<' MAIN_INTERPRETER_LOOP'; @@@ int @@@ runops() { @@@ SAVEI32(runlevel); @@@ runlevel++; @@@ while ( op = (*op->op_ppaddr)() ); @@@ TAINT_NOT; @@@ return 0; @@@ } MAIN_INTERPRETER_LOOP
Or with a fixed amount of leading whitespace, with remaining indentation correctly preserved:
my $poem = fix<<EVER_ON_AND_ON; Now far ahead the Road has gone, And I must follow, if I can, Pursuing it with eager feet, Until it joins some larger way Where many paths and errands meet. And whither then? I cannot say. --Bilbo in /usr/src/perl/pp_ctl.c EVER_ON_AND_ON
Beginning with Perl version 5.26, a much simpler and cleaner way to write indented here documents has been added to the language: the tilde (~) modifier. See "Indented Here-docs" in perlop for details.
A list is a fixed collection of scalars. An array is a variable that holds a variable collection of scalars. An array can supply its collection for list operations, so list operations also work on arrays:
# slices ( 'dog', 'cat', 'bird' )[2,3]; @animals[2,3]; # iteration foreach ( qw( dog cat bird ) ) { ... } foreach ( @animals ) { ... } my @three = grep { length == 3 } qw( dog cat bird ); my @three = grep { length == 3 } @animals; # supply an argument list wash_animals( qw( dog cat bird ) ); wash_animals( @animals );
Array operations, which change the scalars, rearrange them, or add or subtract some scalars, only work on arrays. These can't work on a list, which is fixed. Array operations include "shift", "unshift", "push", "pop", and "splice".
An array can also change its length:
$#animals = 1; # truncate to two elements $#animals = 10000; # pre-extend to 10,001 elements
You can change an array element, but you can't change a list element:
$animals[0] = 'Rottweiler'; qw( dog cat bird )[0] = 'Rottweiler'; # syntax error! foreach ( @animals ) { s/^d/fr/; # works fine } foreach ( qw( dog cat bird ) ) { s/^d/fr/; # Error! Modification of read only value! }
However, if the list element is itself a variable, it appears that you can change a list element. However, the list element is the variable, not the data. You're not changing the list element, but something the list element refers to. The list element itself doesn't change: it's still the same variable.
You also have to be careful about context. You can assign an array to a scalar to get the number of elements in the array. This only works for arrays, though:
my $count = @animals; # only works with arrays
If you try to do the same thing with what you think is a list, you get a quite different result.  The comma operator (yes, it's an operator!) in scalar context evaluates its lefthand side, throws away the result, and evaluates it's righthand side and returns the result. In effect, that list-lookalike assigns to $scalar it's rightmost value. Many people mess this up because they choose a list-lookalike whose last element is also the count they expect:
my $scalar = ( 1, 2, 3 ); # $scalar gets 3, accidentally
The difference is the sigil, that special character in front of the array name. The "$" sigil means "exactly one item", while the "@" sigil means "zero or more items".
The confusion arises because people incorrectly assume that the sigil denotes the variable type.
The $array[1] is a single-element access to the array. It's going to return the item in index 1 (or undef if there is no item there). If you intend to get exactly one element from the array, this is the form you should use.
The @array[1] is an array slice, although it has only one index. You can pull out multiple elements simultaneously by specifying additional indices as a list, like @array[1,4,3,0].
Using a slice on the lefthand side of the assignment supplies list context to the righthand side. This can lead to unexpected results. For instance, if you want to read a single line from a filehandle, assigning to a scalar value is fine:
$array[1] = <STDIN>;
However, in list context, the line input operator returns all of the lines as a list. The first line goes into @array[1] and the rest of the lines mysteriously disappear:
@array[1] = <STDIN>; # most likely not what you want
Either the "use warnings" pragma or the -w flag will warn you when you use an array slice with a single index.
Use a hash. When you think the words "unique" or "duplicated", think "hash keys".
If you don't care about the order of the elements, you could just create the hash then extract the keys. It's not important how you create that hash: just that you use "keys" to get the unique elements.
my %hash = map { $_, 1 } @array; # or a hash slice: @hash{ @array } = (); # or a foreach: $hash{$_} = 1 foreach ( @array ); my @unique = keys %hash;
If you want to use a module, try the "uniq" function from List::MoreUtils. In list context it returns the unique elements, preserving their order in the list. In scalar context, it returns the number of unique elements.
use List::MoreUtils qw(uniq); my @unique = uniq( 1, 2, 3, 4, 4, 5, 6, 5, 7 ); # 1,2,3,4,5,6,7 my $unique = uniq( 1, 2, 3, 4, 4, 5, 6, 5, 7 ); # 7
You can also go through each element and skip the ones you've seen before. Use a hash to keep track. The first time the loop sees an element, that element has no key in %Seen. The "next" statement creates the key and immediately uses its value, which is "undef", so the loop continues to the "push" and increments the value for that key. The next time the loop sees that same element, its key exists in the hash and the value for that key is true (since it's not 0 or "undef"), so the next skips that iteration and the loop goes to the next element.
my @unique = (); my %seen = (); foreach my $elem ( @array ) { next if $seen{ $elem }++; push @unique, $elem; }
You can write this more briefly using a grep, which does the same thing.
my %seen = (); my @unique = grep { ! $seen{ $_ }++ } @array;
Hearing the word "in" is an indication that you probably should have used a hash, not a list or array, to store your data. Hashes are designed to answer this question quickly and efficiently. Arrays aren't.
That being said, there are several ways to approach this. In Perl 5.10 and later, you can use the smart match operator to check that an item is contained in an array or a hash:
use 5.010; if( $item ~~ @array ) { say "The array contains $item" } if( $item ~~ %hash ) { say "The hash contains $item" }
With earlier versions of Perl, you have to do a bit more work. If you are going to make this query many times over arbitrary string values, the fastest way is probably to invert the original array and maintain a hash whose keys are the first array's values:
my @blues = qw/azure cerulean teal turquoise lapis-lazuli/; my %is_blue = (); for (@blues) { $is_blue{$_} = 1 }
Now you can check whether $is_blue{$some_color}. It might have been a good idea to keep the blues all in a hash in the first place.
If the values are all small integers, you could use a simple indexed array. This kind of an array will take up less space:
my @primes = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31); my @is_tiny_prime = (); for (@primes) { $is_tiny_prime[$_] = 1 } # or simply @istiny_prime[@primes] = (1) x @primes;
Now you check whether $is_tiny_prime[$some_number].
If the values in question are integers instead of strings, you can save quite a lot of space by using bit strings instead:
my @articles = ( 1..10, 150..2000, 2017 ); undef $read; for (@articles) { vec($read,$_,1) = 1 }
Now check whether "vec($read,$n,1)" is true for some $n.
These methods guarantee fast individual tests but require a re-organization of the original list or array. They only pay off if you have to test multiple values against the same array.
If you are testing only once, the standard module List::Util exports the function "first" for this purpose. It works by stopping once it finds the element. It's written in C for speed, and its Perl equivalent looks like this subroutine:
sub first (&@) { my $code = shift; foreach (@_) { return $_ if &{$code}(); } undef; }
If speed is of little concern, the common idiom uses grep in scalar context (which returns the number of items that passed its condition) to traverse the entire list. This does have the benefit of telling you how many matches it found, though.
my $is_there = grep $_ eq $whatever, @array;
If you want to actually extract the matching elements, simply use grep in list context.
my @matches = grep $_ eq $whatever, @array;
my (@union, @intersection, @difference); my %count = (); foreach my $element (@array1, @array2) { $count{$element}++ } foreach my $element (keys %count) { push @union, $element; push @{ $count{$element} > 1 ? \@intersection : \@difference }, $element; }
Note that this is the symmetric difference, that is, all elements in either A or in B but not in both. Think of it as an xor operation.
use 5.010; if( @array1 ~~ @array2 ) { say "The arrays are the same"; } if( %hash1 ~~ %hash2 ) # doesn't check values! { say "The hash keys are the same"; }
The following code works for single-level arrays. It uses a stringwise comparison, and does not distinguish defined versus undefined empty strings. Modify if you have other needs.
$are_equal = compare_arrays(\@frogs, \@toads); sub compare_arrays { my ($first, $second) = @_; no warnings; # silence spurious -w undef complaints return 0 unless @$first == @$second; for (my $i = 0; $i < @$first; $i++) { return 0 if $first->[$i] ne $second->[$i]; } return 1; }
For multilevel structures, you may wish to use an approach more like this one. It uses the CPAN module FreezeThaw:
use FreezeThaw qw(cmpStr); my @a = my @b = ( "this", "that", [ "more", "stuff" ] ); printf "a and b contain %s arrays\n", cmpStr(\@a, \@b) == 0 ? "the same" : "different";
This approach also works for comparing hashes. Here we'll demonstrate two different answers:
use FreezeThaw qw(cmpStr cmpStrHard); my %a = my %b = ( "this" => "that", "extra" => [ "more", "stuff" ] ); $a{EXTRA} = \%b; $b{EXTRA} = \%a; printf "a and b contain %s hashes\n", cmpStr(\%a, \%b) == 0 ? "the same" : "different"; printf "a and b contain %s hashes\n", cmpStrHard(\%a, \%b) == 0 ? "the same" : "different";
The first reports that both those the hashes contain the same data, while the second reports that they do not. Which you prefer is left as an exercise to the reader.
use List::Util qw(first); my $element = first { /Perl/ } @array;
If you cannot use List::Util, you can make your own loop to do the same thing. Once you find the element, you stop the loop with last.
my $found; foreach ( @array ) { if( /Perl/ ) { $found = $_; last } }
If you want the array index, use the "firstidx()" function from "List::MoreUtils":
use List::MoreUtils qw(firstidx); my $index = firstidx { /Perl/ } @array;
Or write it yourself, iterating through the indices and checking the array element at each index until you find one that satisfies the condition:
my( $found, $index ) = ( undef, -1 ); for( $i = 0; $i < @array; $i++ ) { if( $array[$i] =~ /Perl/ ) { $found = $array[$i]; $index = $i; last; } }
Perl's arrays do not have a fixed size, so you don't need linked lists if you just want to add or remove items. You can use array operations such as "push", "pop", "shift", "unshift", or "splice" to do that.
Sometimes, however, linked lists can be useful in situations where you want to "shard" an array so you have many small arrays instead of a single big array. You can keep arrays longer than Perl's largest array index, lock smaller arrays separately in threaded programs, reallocate less memory, or quickly insert elements in the middle of the chain.
Steve Lembark goes through the details in his YAPC::NA 2009 talk "Perly Linked Lists" ( <http://www.slideshare.net/lembark/perly-linked-lists> ), although you can just use his LinkedList::Single module.
If you want to cycle through an array endlessly, you can increment the index modulo the number of elements in the array:
my @array = qw( a b c ); my $i = 0; while( 1 ) { print $array[ $i++ % @array ], "\n"; last if $i > 20; }
You can also use Tie::Cycle to use a scalar that always has the next element of the circular array:
use Tie::Cycle; tie my $cycle, 'Tie::Cycle', [ qw( FFFFFF 000000 FFFF00 ) ]; print $cycle; # FFFFFF print $cycle; # 000000 print $cycle; # FFFF00
The Array::Iterator::Circular creates an iterator object for circular arrays:
use Array::Iterator::Circular; my $color_iterator = Array::Iterator::Circular->new( qw(red green blue orange) ); foreach ( 1 .. 20 ) { print $color_iterator->next, "\n"; }
use List::Util 'shuffle'; @shuffled = shuffle(@list);
If not, you can use a Fisher-Yates shuffle.
sub fisher_yates_shuffle { my $deck = shift; # $deck is a reference to an array return unless @$deck; # must not be empty! my $i = @$deck; while (--$i) { my $j = int rand ($i+1); @$deck[$i,$j] = @$deck[$j,$i]; } } # shuffle my mpeg collection # my @mpeg = <audio/*/*.mp3>; fisher_yates_shuffle( \@mpeg ); # randomize @mpeg in place print @mpeg;
Note that the above implementation shuffles an array in place, unlike the "List::Util::shuffle()" which takes a list and returns a new shuffled list.
You've probably seen shuffling algorithms that work using splice, randomly picking another element to swap the current element with
srand; @new = (); @old = 1 .. 10; # just a demo while (@old) { push(@new, splice(@old, rand @old, 1)); }
This is bad because splice is already O(N), and since you do it N times, you just invented a quadratic algorithm; that is, O(N**2). This does not scale, although Perl is so efficient that you probably won't notice this until you have rather largish arrays.
for (@lines) { s/foo/bar/; # change that word tr/XZ/ZX/; # swap those letters }
Here's another; let's compute spherical volumes:
my @volumes = @radii; for (@volumes) { # @volumes has changed parts $_ **= 3; $_ *= (4/3) * 3.14159; # this will be constant folded }
which can also be done with "map()" which is made to transform one list into another:
my @volumes = map {$_ ** 3 * (4/3) * 3.14159} @radii;
If you want to do the same thing to modify the values of the hash, you can use the "values" function. As of Perl 5.6 the values are not copied, so if you modify $orbit (in this case), you modify the value.
for my $orbit ( values %orbits ) { ($orbit **= 3) *= (4/3) * 3.14159; }
Prior to perl 5.6 "values" returned copies of the values, so older perl code often contains constructions such as @orbits{keys %orbits} instead of "values %orbits" where the hash is to be modified.
my $index = rand @array; my $element = $array[$index];
Or, simply:
my $element = $array[ rand @array ];
use Algorithm::Permute; my @array = 'a'..'d'; my $p_iterator = Algorithm::Permute->new ( \@array ); while (my @perm = $p_iterator->next) { print "next permutation: (@perm)\n"; }
For even faster execution, you could do:
use Algorithm::Permute; my @array = 'a'..'d'; Algorithm::Permute::permute { print "next permutation: (@array)\n"; } @array;
Here's a little program that generates all permutations of all the words on each line of input. The algorithm embodied in the "permute()" function is discussed in Volume 4 (still unpublished) of Knuth's The Art of Computer Programming and will work on any list:
#!/usr/bin/perl -n # Fischer-Krause ordered permutation generator sub permute (&@) { my $code = shift; my @idx = 0..$#_; while ( $code->(@_[@idx]) ) { my $p = $#idx; --$p while $idx[$p-1] > $idx[$p]; my $q = $p or return; push @idx, reverse splice @idx, $p; ++$q while $idx[$p-1] > $idx[$q]; @idx[$p-1,$q]=@idx[$q,$p-1]; } } permute { print "@_\n" } split;
The Algorithm::Loops module also provides the "NextPermute" and "NextPermuteNum" functions which efficiently find all unique permutations of an array, even if it contains duplicate values, modifying it in-place: if its elements are in reverse-sorted order then the array is reversed, making it sorted, and it returns false; otherwise the next permutation is returned.
"NextPermute" uses string order and "NextPermuteNum" numeric order, so you can enumerate all the permutations of 0..9 like this:
use Algorithm::Loops qw(NextPermuteNum); my @list= 0..9; do { print "@list\n" } while NextPermuteNum @list;
@list = sort { $a <=> $b } @list;
The default sort function is cmp, string comparison, which would sort "(1, 2, 10)" into "(1, 10, 2)". "<=>", used above, is the numerical comparison operator.
If you have a complicated function needed to pull out the part you want to sort on, then don't do it inside the sort function. Pull it out first, because the sort BLOCK can be called many times for the same element. Here's an example of how to pull out the first word after the first number on each item, and then sort those words case-insensitively.
my @idx; for (@data) { my $item; ($item) = /\d+\s*(\S+)/; push @idx, uc($item); } my @sorted = @data[ sort { $idx[$a] cmp $idx[$b] } 0 .. $#idx ];
which could also be written this way, using a trick that's come to be known as the Schwartzian Transform:
my @sorted = map { $_->[0] } sort { $a->[1] cmp $b->[1] } map { [ $_, uc( (/\d+\s*(\S+)/)[0]) ] } @data;
If you need to sort on several fields, the following paradigm is useful.
my @sorted = sort { field1($a) <=> field1($b) || field2($a) cmp field2($b) || field3($a) cmp field3($b) } @data;
This can be conveniently combined with precalculation of keys as given above.
See the sort article in the "Far More Than You Ever Wanted To Know" collection in <http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz> for more about this approach.
See also the question later in perlfaq4 on sorting hashes.
For example, you don't have to store individual bits in an array (which would mean that you're wasting a lot of space). To convert an array of bits to a string, use "vec()" to set the right bits. This sets $vec to have bit N set only if $ints[N] was set:
my @ints = (...); # array of bits, e.g. ( 1, 0, 0, 1, 1, 0 ... ) my $vec = ''; foreach( 0 .. $#ints ) { vec($vec,$_,1) = 1 if $ints[$_]; }
The string $vec only takes up as many bits as it needs. For instance, if you had 16 entries in @ints, $vec only needs two bytes to store them (not counting the scalar variable overhead).
Here's how, given a vector in $vec, you can get those bits into your @ints array:
sub bitvec_to_list { my $vec = shift; my @ints; # Find null-byte density then select best algorithm if ($vec =~ tr/\0// / length $vec > 0.95) { use integer; my $i; # This method is faster with mostly null-bytes while($vec =~ /[^\0]/g ) { $i = -9 + 8 * pos $vec; push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); push @ints, $i if vec($vec, ++$i, 1); } } else { # This method is a fast general algorithm use integer; my $bits = unpack "b*", $vec; push @ints, 0 if $bits =~ s/^(\d)// && $1; push @ints, pos $bits while($bits =~ /1/g); } return \@ints; }
This method gets faster the more sparse the bit vector is. (Courtesy of Tim Bunce and Winfried Koenig.)
You can make the while loop a lot shorter with this suggestion from Benjamin Goldberg:
while($vec =~ /[^\0]+/g ) { push @ints, grep vec($vec, $_, 1), $-[0] * 8 .. $+[0] * 8; }
Or use the CPAN module Bit::Vector:
my $vector = Bit::Vector->new($num_of_bits); $vector->Index_List_Store(@ints); my @ints = $vector->Index_List_Read();
Bit::Vector provides efficient methods for bit vector, sets of small integers and "big int" math.
Here's a more extensive illustration using vec():
# vec demo my $vector = "\xff\x0f\xef\xfe"; print "Ilya's string \\xff\\x0f\\xef\\xfe represents the number ", unpack("N", $vector), "\n"; my $is_set = vec($vector, 23, 1); print "Its 23rd bit is ", $is_set ? "set" : "clear", ".\n"; pvec($vector); set_vec(1,1,1); set_vec(3,1,1); set_vec(23,1,1); set_vec(3,1,3); set_vec(3,2,3); set_vec(3,4,3); set_vec(3,4,7); set_vec(3,8,3); set_vec(3,8,7); set_vec(0,32,17); set_vec(1,32,17); sub set_vec { my ($offset, $width, $value) = @_; my $vector = ''; vec($vector, $offset, $width) = $value; print "offset=$offset width=$width value=$value\n"; pvec($vector); } sub pvec { my $vector = shift; my $bits = unpack("b*", $vector); my $i = 0; my $BASE = 8; print "vector length in bytes: ", length($vector), "\n"; @bytes = unpack("A8" x length($vector), $bits); print "bits are: @bytes\n\n"; }
There are a couple of ways that you can process an entire hash. You can get a list of keys, then go through each key, or grab a one key-value pair at a time.
To go through all of the keys, use the "keys" function. This extracts all of the keys of the hash and gives them back to you as a list. You can then get the value through the particular key you're processing:
foreach my $key ( keys %hash ) { my $value = $hash{$key} ... }
Once you have the list of keys, you can process that list before you process the hash elements. For instance, you can sort the keys so you can process them in lexical order:
foreach my $key ( sort keys %hash ) { my $value = $hash{$key} ... }
Or, you might want to only process some of the items. If you only want to deal with the keys that start with "text:", you can select just those using "grep":
foreach my $key ( grep /^text:/, keys %hash ) { my $value = $hash{$key} ... }
If the hash is very large, you might not want to create a long list of keys. To save some memory, you can grab one key-value pair at a time using "each()", which returns a pair you haven't seen yet:
while( my( $key, $value ) = each( %hash ) ) { ... }
The "each" operator returns the pairs in apparently random order, so if ordering matters to you, you'll have to stick with the "keys" method.
The "each()" operator can be a bit tricky though. You can't add or delete keys of the hash while you're using it without possibly skipping or re-processing some pairs after Perl internally rehashes all of the elements. Additionally, a hash has only one iterator, so if you mix "keys", "values", or "each" on the same hash, you risk resetting the iterator and messing up your processing. See the "each" entry in perlfunc for more details.
Before you decide to merge two hashes, you have to decide what to do if both hashes contain keys that are the same and if you want to leave the original hashes as they were.
If you want to preserve the original hashes, copy one hash (%hash1) to a new hash (%new_hash), then add the keys from the other hash (%hash2 to the new hash. Checking that the key already exists in %new_hash gives you a chance to decide what to do with the duplicates:
my %new_hash = %hash1; # make a copy; leave %hash1 alone foreach my $key2 ( keys %hash2 ) { if( exists $new_hash{$key2} ) { warn "Key [$key2] is in both hashes!"; # handle the duplicate (perhaps only warning) ... next; } else { $new_hash{$key2} = $hash2{$key2}; } }
If you don't want to create a new hash, you can still use this looping technique; just change the %new_hash to %hash1.
foreach my $key2 ( keys %hash2 ) { if( exists $hash1{$key2} ) { warn "Key [$key2] is in both hashes!"; # handle the duplicate (perhaps only warning) ... next; } else { $hash1{$key2} = $hash2{$key2}; } }
If you don't care that one hash overwrites keys and values from the other, you could just use a hash slice to add one hash to another. In this case, values from %hash2 replace values from %hash1 when they have keys in common:
@hash1{ keys %hash2 } = values %hash2;
The easy answer is "Don't do that!"
If you iterate through the hash with each(), you can delete the key most recently returned without worrying about it. If you delete or add other keys, the iterator may skip or double up on them since perl may rearrange the hash table. See the entry for "each()" in perlfunc.
my %by_value = reverse %by_key; my $key = $by_value{$value};
That's not particularly efficient. It would be more space-efficient to use:
while (my ($key, $value) = each %by_key) { $by_value{$value} = $key; }
If your hash could have repeated values, the methods above will only find one of the associated keys. This may or may not worry you. If it does worry you, you can always reverse the hash into a hash of arrays instead:
while (my ($key, $value) = each %by_key) { push @{$key_list_by_value{$value}}, $key; }
This is very similar to "How do I process an entire hash?", also in perlfaq4, but a bit simpler in the common cases.
You can use the "keys()" built-in function in scalar context to find out have many entries you have in a hash:
my $key_count = keys %hash; # must be scalar context!
If you want to find out how many entries have a defined value, that's a bit different. You have to check each value. A "grep" is handy:
my $defined_value_count = grep { defined } values %hash;
You can use that same structure to count the entries any way that you like. If you want the count of the keys with vowels in them, you just test for that instead:
my $vowel_count = grep { /[aeiou]/ } keys %hash;
The "grep" in scalar context returns the count. If you want the list of matching items, just use it in list context instead:
my @defined_values = grep { defined } values %hash;
The "keys()" function also resets the iterator, which means that you may see strange results if you use this between uses of other hash operators such as "each()".
To sort a hash, start with the keys. In this example, we give the list of keys to the sort function which then compares them ASCIIbetically (which might be affected by your locale settings). The output list has the keys in ASCIIbetical order. Once we have the keys, we can go through them to create a report which lists the keys in ASCIIbetical order.
my @keys = sort { $a cmp $b } keys %hash; foreach my $key ( @keys ) { printf "%-20s %6d\n", $key, $hash{$key}; }
We could get more fancy in the "sort()" block though. Instead of comparing the keys, we can compute a value with them and use that value as the comparison.
For instance, to make our report order case-insensitive, we use "lc" to lowercase the keys before comparing them:
my @keys = sort { lc $a cmp lc $b } keys %hash;
Note: if the computation is expensive or the hash has many elements, you may want to look at the Schwartzian Transform to cache the computation results.
If we want to sort by the hash value instead, we use the hash key to look it up. We still get out a list of keys, but this time they are ordered by their value.
my @keys = sort { $hash{$a} <=> $hash{$b} } keys %hash;
From there we can get more complex. If the hash values are the same, we can provide a secondary sort on the hash key.
my @keys = sort { $hash{$a} <=> $hash{$b} or "\L$a" cmp "\L$b" } keys %hash;
Pictures help... Here's the %hash table:
keys values +------+------+ | a | 3 | | x | 7 | | d | 0 | | e | 2 | +------+------+
And these conditions hold
$hash{'a'} is true $hash{'d'} is false defined $hash{'d'} is true defined $hash{'a'} is true exists $hash{'a'} is true (Perl 5 only) grep ($_ eq 'a', keys %hash) is true
If you now say
undef $hash{'a'}
your table now reads:
keys values +------+------+ | a | undef| | x | 7 | | d | 0 | | e | 2 | +------+------+
and these conditions now hold; changes in caps:
$hash{'a'} is FALSE $hash{'d'} is false defined $hash{'d'} is true defined $hash{'a'} is FALSE exists $hash{'a'} is true (Perl 5 only) grep ($_ eq 'a', keys %hash) is true
Notice the last two: you have an undef value, but a defined key!
Now, consider this:
delete $hash{'a'}
your table now reads:
keys values +------+------+ | x | 7 | | d | 0 | | e | 2 | +------+------+
and these conditions now hold; changes in caps:
$hash{'a'} is false $hash{'d'} is false defined $hash{'d'} is true defined $hash{'a'} is false exists $hash{'a'} is FALSE (Perl 5 only) grep ($_ eq 'a', keys %hash) is FALSE
See, the whole entry is gone!
You can use the "keys" or "values" functions to reset "each". To simply reset the iterator used by "each" without doing anything else, use one of them in void context:
keys %hash; # resets iterator, nothing else. values %hash; # resets iterator, nothing else.
See the documentation for "each" in perlfunc.
my %seen = (); for my $element (keys(%foo), keys(%bar)) { $seen{$element}++; } my @uniq = keys %seen;
Or more succinctly:
my @uniq = keys %{{%foo,%bar}};
Or if you really want to save space:
my %seen = (); while (defined ($key = each %foo)) { $seen{$key}++; } while (defined ($key = each %bar)) { $seen{$key}++; } my @uniq = keys %seen;
use Tie::IxHash; tie my %myhash, 'Tie::IxHash'; for (my $i=0; $i<20; $i++) { $myhash{$i} = 2*$i; } my @keys = keys %myhash; # @keys = (0,1,2,3,...)
Are you using a really old version of Perl?
Normally, accessing a hash key's value for a nonexistent key will not create the key.
my %hash = (); my $value = $hash{ 'foo' }; print "This won't print\n" if exists $hash{ 'foo' };
Passing $hash{ 'foo' } to a subroutine used to be a special case, though. Since you could assign directly to $_[0], Perl had to be ready to make that assignment so it created the hash key ahead of time:
my_sub( $hash{ 'foo' } ); print "This will print before 5.004\n" if exists $hash{ 'foo' }; sub my_sub { # $_[0] = 'bar'; # create hash key in case you do this 1; }
Since Perl 5.004, however, this situation is a special case and Perl creates the hash key only when you make the assignment:
my_sub( $hash{ 'foo' } ); print "This will print, even after 5.004\n" if exists $hash{ 'foo' }; sub my_sub { $_[0] = 'bar'; }
However, if you want the old behavior (and think carefully about that because it's a weird side effect), you can pass a hash slice instead. Perl 5.004 didn't make this a special case:
my_sub( @hash{ qw/foo/ } );
$record = { NAME => "Jason", EMPNO => 132, TITLE => "deputy peon", AGE => 23, SALARY => 37_000, PALS => [ "Norbert", "Rhys", "Phineas"], };
References are documented in perlref and perlreftut. Examples of complex data structures are given in perldsc and perllol. Examples of structures and object-oriented classes are in perlootut.
Hash keys are strings, so you can't really use a reference as the key. When you try to do that, perl turns the reference into its stringified form (for instance, "HASH(0xDEADBEEF)"). From there you can't get back the reference from the stringified form, at least without doing some extra work on your own.
Remember that the entry in the hash will still be there even if the referenced variable goes out of scope, and that it is entirely possible for Perl to subsequently allocate a different variable at the same address. This will mean a new variable might accidentally be associated with the value for an old.
If you have Perl 5.10 or later, and you just want to store a value against the reference for lookup later, you can use the core Hash::Util::Fieldhash module. This will also handle renaming the keys if you use multiple threads (which causes all variables to be reallocated at new addresses, changing their stringification), and garbage-collecting the entries when the referenced variable goes out of scope.
If you actually need to be able to get a real reference back from each hash entry, you can use the Tie::RefHash module, which does the required work for you.
The trick to this problem is avoiding accidental autovivification. If you want to check three keys deep, you might naievely try this:
my %hash; if( exists $hash{key1}{key2}{key3} ) { ...; }
Even though you started with a completely empty hash, after that call to "exists" you've created the structure you needed to check for "key3":
%hash = ( 'key1' => { 'key2' => {} } );
That's autovivification. You can get around this in a few ways. The easiest way is to just turn it off. The lexical "autovivification" pragma is available on CPAN. Now you don't add to the hash:
{ no autovivification; my %hash; if( exists $hash{key1}{key2}{key3} ) { ...; } }
The Data::Diver module on CPAN can do it for you too. Its "Dive" subroutine can tell you not only if the keys exist but also get the value:
use Data::Diver qw(Dive); my @exists = Dive( \%hash, qw(key1 key2 key3) ); if( ! @exists ) { ...; # keys do not exist } elsif( ! defined $exists[0] ) { ...; # keys exist but value is undef }
You can easily do this yourself too by checking each level of the hash before you move onto the next level. This is essentially what Data::Diver does for you:
if( check_hash( \%hash, qw(key1 key2 key3) ) ) { ...; } sub check_hash { my( $hash, @keys ) = @_; return unless @keys; foreach my $key ( @keys ) { return unless eval { exists $hash->{$key} }; $hash = $hash->{$key}; } return 1; }
Also see "binmode" in perlfunc or perlopentut.
If you're concerned about 8-bit textual data then see perllocale. If you want to deal with multibyte characters, however, there are some gotchas. See the section on Regular Expressions.
use 5.010; if ( /\D/ ) { say "\thas nondigits"; } if ( /^\d+\z/ ) { say "\tis a whole number"; } if ( /^-?\d+\z/ ) { say "\tis an integer"; } if ( /^[+-]?\d+\z/ ) { say "\tis a +/- integer"; } if ( /^-?(?:\d+\.?|\.\d)\d*\z/ ) { say "\tis a real number"; } if ( /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i ) { say "\tis a C float" }
There are also some commonly used modules for the task. Scalar::Util (distributed with 5.8) provides access to perl's internal function "looks_like_number" for determining whether a variable looks like a number. Data::Types exports functions that validate data types using both the above and other regular expressions. Thirdly, there is Regexp::Common which has regular expressions to match various types of numbers. Those three modules are available from the CPAN.
If you're on a POSIX system, Perl supports the "POSIX::strtod" function for converting strings to doubles (and also "POSIX::strtol" for longs). Its semantics are somewhat cumbersome, so here's a "getnum" wrapper function for more convenient access. This function takes a string and returns the number it found, or "undef" for input that isn't a C float. The "is_numeric" function is a front end to "getnum" if you just want to say, "Is this a float?"
sub getnum { use POSIX qw(strtod); my $str = shift; $str =~ s/^\s+//; $str =~ s/\s+$//; $! = 0; my($num, $unparsed) = strtod($str); if (($str eq '') || ($unparsed != 0) || $!) { return undef; } else { return $num; } } sub is_numeric { defined getnum($_[0]) }
Or you could check out the String::Scanf module on the CPAN instead.
use Storable; store(\%hash, "filename"); # later on... $href = retrieve("filename"); # by ref %hash = %{ retrieve("filename") }; # direct to hash
use Storable qw(dclone); $r2 = dclone($r1);
Where $r1 can be a reference to any kind of data structure you'd like. It will be deeply copied. Because "dclone" takes and returns references, you'd have to add extra punctuation if you had a hash of arrays that you wanted to copy.
%newhash = %{ dclone(\%oldhash) };
You can use the "UNIVERSAL" class (see UNIVERSAL). However, please be very careful to consider the consequences of doing this: adding methods to every object is very likely to have unintended consequences. If possible, it would be better to have all your object inherit from some common base class, or to use an object system like Moose that supports roles.
See <https://metacpan.org/release/PGPLOT> for the code.
This documentation is free; you can redistribute it and/or modify it under the same terms as Perl itself.
Irrespective of its distribution, all code examples in this file are hereby placed into the public domain. You are permitted and encouraged to use this code in your own programs for fun or for profit as you see fit. A simple comment in the code giving credit would be courteous but is not required.
| 2019-10-21 | perl v5.30.3 |


Svelte components for Iconify Icon Finder
This tutorial is part of Iconify Icon Finder packages tutorial.
Branch "base-svelte" of Iconify Icon Finder contains set of Svelte components and stylesheet.
It contains full set of components you need to build custom icon picker.
Contents
What is in package?
- Customisable build scripts.
- Components that are responsible for displaying data to visitor. They rely on Icon Finder Core to do all the heavy work, such as sending API queries and parsing data.
- Stylesheet that is built with SASS.
Examples
Few examples of projects that are based on Icon Finder Svelte components. See projects based on Iconify Icon Finder Svelte components.
Build scripts
Build scripts are designed to be easy to customise. You can:
- Change locations and names of built files.
- Completely ignore stylesheet and rely on your own instead.
- Add your own stuff to build, such as bundling it all or script to build a plug-in.
You can find build configuration in build/config.js. There you can change various filenames. See comments.
You can add custom build scripts to build process by editing build/all.js.
Components
Components are written in Svelte. Why no React or Vue? Because:
- Svelte is lighter.
- Built package does not have dependencies, making it easier to integrate in any environment, even as Vue or React components.
Some components have multiple versions, which you can swap in configuration files.
See components configuration documentation for details.
Stylesheet
Stylesheet is a basic SASS stylesheet.
Main entry is src/style-iconify/style.scss. You can change it in build/config.js.
If you are changing stylesheet, you also need to change components configuration in src/icon-finder/config/theme.ts.
See theme configuration documentation for details.


{% extends "layout.html" %} {% block title %}{{ _("Send a Postcard") }} —{% endblock %} {% block content %}
{{ _("You will be given a profile with an address. Please send them a postcard.") }}


Draggy is a lightweight jQuery plugin that allows to conveniently create GMail style scrollbars.
Using Draggy in your project is simple: just include jquery.draggy.js and jquery.draggy.css in your HTML page and invoke following code:
$('#my-element').draggy();
The Ice and Fire series is generally praised for its realism and incredibly expansive world.[67] Believing that magic should be used moderately in the epic fantasy genre,[17] George R. R. Martin set out to make the story feel more like historical fiction than contemporary fantasy, with less emphasis on magic and sorcery in favor of battles, political intrigue and the characters.[16] With the amount of magic gradually increasing from the start, the series is still to end with less overt magic than most contemporary fantasies.[26] In Martin's eyes, literary effective magic needs to represent strange and dangerous forces beyond human comprehension,[49] not advanced alien technologies or formulaic spells.[76] As such, the characters understand only the natural aspects of their world, but not the magical elements like the Others.[67]
Since Martin drew on historical sources to build the Ice and Fire world, The Guardian saw a strong resemblance between Westeros and England in the period of the Wars of the Roses.[77] The Atlantic regarded A Song of Ice and Fire as "more a story of politics than one of heroism, a story about humanity wrestling with its baser obsessions than fulfilling its glorious potential" where the emergent power struggle stems from the feudal system's repression and not from the fight between good and evil.[73] Martin not only wanted to reflect the frictions of the medieval class structures in the novels, but also explore the consequences of the leaders' decisions, as general goodness does not automatically make competent leaders and vice versa.[57] A common theme in the fantasy genre is the battle between good and evil,[57] which Martin rejects for not mirroring the real world.[22] Attracted to gray characters instead of orcs and angels,[78] Martin instead endorses Nobel Prize laureate William Faulkner's view that only the human heart in conflict with itself was worth writing about.[57] Just like people's capacity for good and for evil in real life, Martin explores the questions of redemption and character change in the Ice and Fire series.[79] The multiple viewpoint structure allows characters to be explored from many sides so that, unlike lots of other fantasy, the supposed villains can provide their viewpoint.[61] The reader may then decide about good and evil through the novels' actions and politics.[31] Main characters are killed off so that the reader will not expect the supposed hero to come through unscathed and instead feel the character's fear with each page turn.[25] The novels are also to reflect the substantial death rates in war.[55] The deaths of supernumerary extras or orcs have no major effect on readers, whereas a friend's death has much more emotional impact.[69] Martin prefers a hero's sacrifice to say something profound about human nature.[18]
You can invoke draggy on any DOM element you like. Draggy will automatically calculate if the element is overflowing out of it's parent's dimensions and attach scrollbars accordingly.
When target width is greater than it's parent width, draggy will attach a horizontal scrollbar with the parent.
When target height is greater than it's parent height, draggy will attach a vertical scrollbar with the parent.
When target width and height are greater than it's parent's width and height, draggy will attach horizontal and vertical scrollbars with the parent.
As shown before, applying draggy is simple:
$(selector).draggy();
IMPORTANT: Draggy should be instantiated on an element after all of it's content has been loaded. So if the element contains any images, draggy should be instantiated on it after images have been loaded. jQuery's $(document).ready(callback) invokes a callback when only DOM has been loaded; it doesn't wait for images. Thankfully, we have another function, $(window).load(callback) which invokes the callback after all of it's images have been downloaded.
$(selector).draggy('kill');
Draggy is highly configurable. You can easily tweak it's behavior using one of the following properties. To apply a property, simply pass it on with a value in constructor.
$(selector).draggy({ 'draggability' : 'both' });
It requires jquery.mousewheel.js.
For now, you can associate arrowkeys with only one instance of draggy on a page. If you try to associate arrowkeys with multiple instances, they will only work for the instance they got associated with in the last.
Following are the features that I wish to add to draggy in future:
If I have missed anything do let me know, I would gladly add it to this list.
Your feedback/suggestions are very important so please feel free to write to me at umar dot mughal 2 at gmail dot com. If you find any bug in draggy, please take a moment to report it to github.
Developed by Umar Ashfaq | Report an issue / Request a feature


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IHC issues notice to federal govt over Tezgam train inferno
by Saqib BashirISLAMABAD: The Islamabad High Court on Friday issued a notice to the federal government over the Tezgam train incident.
A single-judge bench presided by Justice Mohsin Akhtar Kiyani heard a petition seeking the removal of Minister of Railways Sheikh Rashid Ahmed and an independent inquiry under the Pakistan Commissioner Inquiry Act 2017 for the October 31 tragedy.
Referring to Ahmed’s claim that the fire was a result of passengers attempting to cook food using a cylinder in the moving train, the petition sought “hearing of both parties” under Section 24-A of the General Clauses Act 1897.
“Moreover a man who believes unilateral view is not righteous within the definition of Article 62(I) (1) of the 1973 Constitution,” stated the petition, adding that the railways minister had lost “legal, religious, ethical and constitutional” justification to remain in office after believing in one side view – that of the train officials – and officiating a response without the completion of the inquiry.
The petitioner also asked why Prime Minister Imran Khan had not sought Ahmed’s resignation yet. “In the past, PM Imran had urged for ministers to resign to ensure transparent inquiries,” he informed the high court.
“Improvements always come with the realisation of shortcomings and strong commitment to overcome these but the unilateral stance of Railway Minister before the inquiry result has made it impossible to fix the liability of Tezgam inferno incident on the Railway officials,” reads the petition. He stressed that no ‘meaningful’ reforms could take place in such a situation.
“The promise to pay compensation to the legal heirs of the deceased and injured would remain a political commitment as there are many examples where promises are yet to be honoured.”
The train tragedy
At least 75 people died in the Tezgam incident. Railways officials said some of the train’s passengers were cooking breakfast around dawn when two of their gas cylinders exploded, sending flames racing through three carriages as the train passed near Rahim Yar Khan in Punjab.
One of the carriages — Wagon No.12 — was carrying mainly people from Mirpurkhas, the town’s deputy commissioner, Attaullah Shah, told AFP. “There was never such a tragic incident to happen to Mirpurkhas.”
The Ministry of Railways suspended six officers for alleged negligence in the aftermath of the Tezgam Express tragedy.


pip_services3_container.ProcessContainer module¶
pip_services3_container.ProcessContainer¶
Process container implementation.
- copyright
Conceptual Vision Consulting LLC 2018-2019, see AUTHORS for more details.
- license
MIT, see LICENSE for more details.
-
class
pip_services3_container.ProcessContainer.
ProcessContainer
(name: str = None, description: str = None)¶ Bases:
pip_services3_container.Container.Container
Inversion of control (IoC) container that runs as a system process. It processes command line arguments and handles unhandled exceptions and Ctrl-C signal to gracefully shutdown the container.
- ### Command line arguments ###
–config -c path to JSON or YAML file with container configuration (default: “./config/config.yml”)
–param –params -p value(s) to parameterize the container configuration
–help -h prints the container usage help
Example:
container = ProcessContainer() container.add_factory(MyComponentFactory()) container.run()
-
run
()¶ Runs the container by instantiating and running components inside the container.
It reads the container configuration, creates, configures, references and opens components. On process exit it closes, unreferences and destroys components to gracefully shutdown.


Ocean [bb10], ocean, in Crystal Sea
Last updated Turn #138
Ocean [bb10], ocean, in Crystal Sea
------------------------------------------------------------------------
4: The Savvy Aardvark [ha5r], ship, 2 hulls, 1 rowing port, 6 sails,
4: 22% damaged, arrived from Ocean [bb11], owner:
4: Phantasm [n4b], Imperial Empire, duke, with two workers,
4: eight sailors
5: The Savvy Aardvark [ha5r], ship, 2 hulls, 1 rowing port, 6 sails,
5: 22% damaged, departed for Ocean [bb09].
Routes leaving Ocean:
North, to Ocean [ba10], 6 days
East, to Ocean [bb11], 6 days
South, to Ocean [bc10], 6 days
West, to Ocean [bb09], 6 days


{% extends "base.html" %} {% load static %} {% block title %}Password Reset Successful{% endblock %} {% block local_css %} {% endblock %} {% block content %}
Your password has been reset. You may now log in.


Computer Scientist by day, starving artist by night
Graduated from University of Victoria in 2017. Spending time learning more programming languages and finding balance between work and creativity.
Creative Outlets
I have explored my creativity in many ways:
Painting on stretched canvases to painting warhammer miniatures.
Playing with 3d printers
Video Games
Collaborative writing
University of Victoria
Bachelor of Science: Combined Major in Computer Science and Visual Arts
Attended: September 2013 to June 2017
Graduated as of November 2017


Intro
One of my PhD projects investigates the impact that songs have on meritocratic beliefs and social inequalities. One of the things that I would like to explore is the potential impact that certain words have when sung in a specific chord. This idea comes from the well-know effect that music (in terms of sounds) has on emotions (Arjmand, Hohagen, Paton, & Rickard 2014) and from the consideration that beliefs are intrinsically multi-sensory. That is, when asking people about their beliefs, the question inevitabily taps the perceptual information that has been encoded and stored during previous experiences. But this is another story.
While thinking through the theoretical aspects, I also spent sometime working the first lines of code to get the data aligned with the way I was thinking. In this process, I encountered the R package chorrrds
, built to extract chords from the website Cifraclub. Building upon the functions of this package, I implemented two functions that allow to match the words of a song with the corresponding chords in which these words are sung. In this blog post, I will explain the features of these two functions and how to use them in a practical example.
Preliminaries
The package chorrrds
can be installed from CRAN, with
install.packages("chorrrds")
and for the latest version, from GitHub with:
# install.packages("devtools")
devtools::install_github("r-music/chorrrds")
Function 1: create_dat
Generally, this is how a song looks on the internet (specifically, on Cifraclub):As you can see, each verse is sung with one or more chords. The problem is how to match each word with the corresponding chord in which they are played. For example, in the first verse, “The best song wasn’t the single, but you weren’t either”, the words “The best song wasn’t” are played in A, “the single, but you weren’t” are played in C, and “either” is in G. How to connect each of these words with the corresponding chords A, C, G?  That is, it does not match words with the respective chords. create_net
does the job. The idea is to search for each chord the beginning of the closest word, and to store all the words that are present before the end of the verse or the beginning of the next chord. Running:
create_net(chords.dat)
creates the intended output:
## # A tibble: 75 x 2
## chord lyric
## <chr> <chr>
## 1 A The best song wasn't
## 2 C the single, but you weren't
## 3 G either
## 4 D Livin' in Ladera Heights, the black Beverl
## 5 A Hills
## 6 C Domesticated paradise, palm trees
## 7 G and pools
## 8 D The water's blue, swallow the pill
## 9 A Keepin' it surreal, whatever
## 10 C you like
## 11 G Whatever feels good, whateve
## 12 D takes you mountain high
## 13 A Keepin' it surreal, not
## 14 C sugar free
## 15 G My TV ain't HD, that's too real
## 16 D Grapevine, mango, peaches, and limes, the
## 17 A sweet life
## 18 C The sweet life,
## 19 G sweet life
## 20 D Sweet life, sweet life
## 21 A The sweet, sweet, sweet, sweet life
## 22 C Sweet life, the
## 23 G sweet life
## 24 D Sweetie pie
## 25 A You've had a landscaper and a house keepe
## 26 C since you were born
## 27 G The sunshine alway
## 28 D kept you warm
## 29 A So why see the world, when you
## 30 C got the beach
## 31 G Don't know why see the world, when you
## 32 D got the beach
## 33 A The sweet life
## 34 C The best song wasn't the single, but you couldn't turn
## 35 G your radio down
## 36 D Satellite need a receiver, can't seem
## 37 A to turn the signal fully off
## 38 C Transmitting
## 39 G the waves
## 40 D You're catching that breeze 'til you're dead in the grave
## 41 A But you're keepin' it surreal, whatever
## 42 C you like
## 43 G Whatever feels good, whateve
## 44 D takes you mountain high
## 45 A Keepin' it surreal, not
## 46 C sugar free, my tv ain't HD, that's
## 47 G too real
## 48 D Grapevines, mango, peaches, and lime, a sweet life
## 49 C Live and die in the
## 50 G life
## 51 A You've had a landscaper and a house keepe
## 52 C since you were born, yeah
## 53 G The sunshine alway
## 54 D kept you warm
## 55 A So why see the world, when you
## 56 C got the beach
## 57 G Don't know why see the world, when you
## 58 D got the beach
## 59 A And the water, is exactly what
## 60 C I wanted
## 61 G It's everything I thought it
## 62 D would be (thought it would be)
## 63 A But this neighborhood is gettin
## 64 C trippier every day
## 65 G The neighborhood is
## 66 D goin' ape shit crazy
## 67 A You've had a landscaper and a house keepe
## 68 C since you were born
## 69 G The sunshine alway
## 70 D kept you warm
## 71 A So why see the world, when you
## 72 C got the beach
## 73 G Don't know why see the world, when you
## 74 D got the beach
## 75 A The sweet life
Note that create_net
builds upon the structure created with create_dat
.
Usage
These functions can be very useful for text, network, and many others types of analyses. For example, it could be useful for a network viz. In the next steps I will only show the final output, you can find the full syntax here.
One thing that could be interesting to visualize is the connections that words have when played in the same chord. In other words, the network we will represent will be made by words connected to each other when played in the same chord. There are four steps to follow: create the edgelist, where words are connected when played in the same chord, create the network with these connections, visualize the network, and take some descriptive information out of this visualization.

## Network attributes:
## vertices = 141
## directed = FALSE
## hyper = FALSE
## loops = FALSE
## multiple = FALSE
## bipartite = FALSE
## total edges= 26252
## missing edges= 0
## non-missing edges= 26252
##
## Vertex attribute names:
## vertex.names
##
## Edge attribute names not shown
- Plot the network!
Let’s have some descriptive information out of this visualization. For example, is the network partitioned in groups? Since words are connected with each other when played in the same chord, it could is plausible to reason that they are played together because meant to express similar feelings or emotions, or for other patterns that the artist wants to convey. To extract this information, we can use the concept of modularity, which goes from 0 to 1 and states that “the possible existence of clusters is revealed by the comparison between the actual density of edges in a subgraph and the density one would expect to have in the subgraph if the vertices of the graph were attached regardless of community structure.” (Fortunato, 2010, p. 89)
library(tidyverse)
library(igraph)
chords.dat <- chorrrds::create_dat("Frank Ocean", "Sweet Life")
chords.net <- chorrrds::create_net(chords.dat)
network <- as.data.frame(matrix(nrow = 2000, # number of words in the song
ncol = 2))
names(network) <- c("chord", "lyric")
for (i in 1:nrow(chords.net)) { # verses
for (j in 1:stringr::str_count(chords.net[i,2], "\\w+")) { # words
network[ match(as.numeric(do.call(paste0, expand.grid(i,j))),
sort(as.numeric(do.call(paste0, expand.grid(1:nrow(chords.net), 1:max(apply(chords.net, 1, function(x) stringr::str_count(x[2], "\\w+")))))))), 1] <- chords.net[i, 1]
network[ match(as.numeric(do.call(paste0, expand.grid(i,j))),
sort(as.numeric(do.call(paste0, expand.grid(1:nrow(chords.net), 1:max(apply(chords.net, 1, function(x) stringr::str_count(x[2], "\\w+")))))))), 2] <- unlist(stringr::str_split(chords.net$lyric[i], " "))[j]
}
}
network <- network %>% na.omit
edgelist <- network %>%
inner_join(., select(., chord, lyric), by = "chord") %>%
filter(lyric.x != lyric.y) %>%
.[, 2:3]
inet <- igraph::graph_from_data_frame(edgelist, directed = F)
mod <- graph_from_edgelist(as.matrix(edgelist[, c(1:2)]), directed = FALSE)
mod2 <- cluster_louvain(mod)
modularity(mod, membership(mod2))
## [1] 0.3184173
According to Newman & Girvan (2004), a minimum threshold to detect the partitioning of a graph is 0.3, with typical values ranging from 0.3 to 0.7. The value of 0.32 shows that, indeed, the words of this song seem to be clustered when the chord in which they are played is taken into account. This could mean many things, for example that words are played in a certain chord because they are generally linked to positive or negative sentiments (e.g., Brand, Acerbi, & Mesoudi, 2019). Since chords themselves could be put on an emotional axis – with minor chords linked to negative emotions and major chords to positive emotions – interesting patterns could emerge from this type of analyses.
Conclusion
The introduction of these two new functions could be an interesting addition to users of the chorrrds
package, adding flexibility to explore the connections between lyrics and chords in different types of analyses. Enjoy!
A special thanks to Bruna Wundervald, the developer of the chorrrds
package, for the help and for the inclusion of these functions in her package :)
Another special thanks to Edo for the help during the code writing process :)
P.S. I am not a programmer, so (1) the code looks bad, and (2) it might have issues. So, if you encounter any problem with the functions, want to give suggestions about how to improve the code, or just want to rant about stuff, drop me a line (lucacarbone@gmail.com)! I’ll be happy to further break my head around it.
Bibliography
Arjmand, H.-A., Hohagen, J., Paton, B., & Rickard, N. S. (2017). Emotional Responses to Music: Shifts in Frontal Brain Asymmetry Mark Periods of Musical Change. Frontiers in Psychology, 8. DOI
Brand, C., Acerbi, A., & Mesoudi, A. (2019). Cultural evolution of emotional expression in 50 years of song lyrics. Evolutionary Human Sciences, 1, E11. DOI
Fortunato, S. (2010). Community detection in graphs. Physics Report, 75–174. DOI
Newman, M., & Girvan, M. (2004). Finding and evaluating community structure in networks. Physical, Review, 1-15. DOI


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| SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |
public interface ICount
Exposes API's to get count of the number of times that X is not NULL in a group. The count(*) function (with no arguments) returns the total number of rows in the group.
| Field Summary | |
|---|---|
static java.lang.String |
INTERFACE_NAME
|
| Method Summary | |
|---|---|
ICountClause |
and(java.lang.String column)
Used to specify AND condition between where clause. |
ICount |
column(java.lang.String column)
Used to provide name of column for which count will be calculated. |
ICount |
distinct()
Used to specify DISTINCT condition. |
java.lang.Object |
execute()
Used to get count, this method should be called in last to calculate count. |
ICount |
groupBy(java.lang.String... columns)
Used to specify GROUP BY statement in conjunction with the aggregate functions to group the result-set by one or more columns. |
ICountClause |
having(java.lang.String column)
Used to specify HAVING clause to SQL because the WHERE keyword could not be used with aggregate functions. |
ICount |
havingClause(java.lang.String havingClause)
Used to provide manually created Where clause, instead of using API's. |
ICountClause |
or(java.lang.String column)
Used to specify OR condition between where clause. |
ICountClause |
where(java.lang.String column)
Column name of which condition will be specified. |
ICount |
whereClause(java.lang.String whereClause)
Used to provide manually created Where clause, instead of using API's. |
| Field Detail |
|---|
static final java.lang.String INTERFACE_NAME
| Method Detail |
|---|
ICount distinct()
ICountClause where(java.lang.String column)
column
- Name of column.
ICount whereClause(java.lang.String whereClause)
whereClause
- Manually created where clause.
ICountClause and(java.lang.String column)
column
- Name of column on which condition need to be specified.
ICountClause or(java.lang.String column)
column
- Name of column on which condition need to be specified.
ICount groupBy(java.lang.String... columns)
columns
- Name of columns.
ICountClause having(java.lang.String column)
column
- Name of column on which condition need to be applied.
ICount havingClause(java.lang.String havingClause)
havingClause
- Where clause.
ICount column(java.lang.String column)
column
- Name of column.
java.lang.Object execute() throws DatabaseException
DatabaseException
- Throws exception if any error occur while calculating count.
|
Apache License 2.0 | ||||||||
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| DOSE: |
25 mg |
oral |
DiPT |
(powder / crystals) |
Recently, I tried 25 mg of diisopropyltryptamine, DIPT. It's something I'd wanted to try for quite a while, after reading about it in TIHKAL, but it always seemed mostly like a novelty, so I wasn't in a big hurry to search for some. A friend had a bunch that he'd gotten about two weeks earlier, and which he and a few others had tried. He generously gave me about 150 mg of it.
This friend had tried a larger dose, I can't remember exactly how much, but I believe it was 75 mg, though it may have been a bit less.  Things went well initially, and he was enjoying this mini-party with totally whacked auditory perceptions, but he said that eventually it got very unsettling and disorienting, and he had to leave. Whether this was the DIPT alone or the DIPT in combination with lots of marijuana was not clear.
So, I decided that 25 mg would be a much more reasonable starting point. Almost all the DIPT reports that can be found, whether in TIHKAL or online, consistently say that it gives a generally good body feeling, absurd audio effects, and not much else. So I was not expecting a major trip, or to be psychedelically incapacitated, or to have my mind blown. I was expecting some kind of twisted entertainment.
After 45-60 minutes, I started to notice changes in the character of sounds. At this point I couldn't really identify the changes, just that something was different. Pretty quickly, within the next 15-30 minutes, it became much more obvious that pitches were shifted downwards. I talked with some people, and their voices were deep and resonant. There was a comical disconnection between watching someone's face as they spoke and hearing their voice, because it felt like some strange soundtrack had been overdubbed over their usual voices. Also, sounds that were deeper also seemed a little more full and powerful.
I felt generally good. There was a bit of a body buzz. If I'd only been experiencing the pitch shifting, I think it would be very hard to identify DIPT as a psychedelic, but I recognized the body sensations as psychedelic. But that was about all there was. At t+1:45 or so, I flipped through the Book of the SubGenius and read for a while, and I had no problem reading the words on the page (i.e. there were no visuals) and I had no problem comprehending the text. If anything, the Book of the SubGenius made slightly more sense than usual, but maybe that was just because I was reading the section on drugs.
Then I listened to some music. This was not as much fun as I'd hoped. The problem was that not only were pitches shifted downwards, they were also out of tune with each other. Chords did not match. It was at about the edge of tolerable, so I listened for a while and managed to enjoy it, mostly because I kept hearing new and strange things as the music changed. One thing which I really noticed is that no matter how much you know and expect things to sound strange, when a new track starts or there's a change in the flow of the music, it all sounds totally bizarre all over again. You hear a track end, and by that time you're mostly used to hearing things shifted lower, and then there's a three second pause and BAM, the next track starts and it's just too weird for words.
At maybe t+4 or t+5 the DIPT started to wear off. This was very subtle. Around this time I'd started smoking some cannabis, and this had only minimal effects on the DIPT. I went to sleep soon after that with no trouble. But sounds were still abnormal when I fell asleep.
The next day I woke up and sat down at my computer. It beeped. It was not a normal beep... it was too low. But everything else sounded fine. Music, people's voices, etc. were all fine, but whenever I heard a mostly pure tone that I was familiar with, like my computer, or my microwave oven, or my watch, it was still just a little bit off. By the next day this was gone too.
I've taken 5-MeO-DIPT a few times. Some of those times, but not all, I have also had audio changes that were very similar to DIPT. 5-MeO-DIPT's audio effects do not seem to be dose-dependent. They were strong my first time at 10 mg, almost nonexistant at 16 mg or so, somewhat there at 13 mg or so, and then not there at all another time at 10 mg. The 5-MeO-DIPT caused pitch shifts that were very similar to DIPT, but they were totally harmonious (and therefore more enjoyable) than DIPT. And when I got those effects, they also lasted through the next day. This is fascinating to me... what is that diisopropyl doing inside my brain? What does it have to do with hearing? Why does it last 24-36 hours, after all the other effects of the drug are long gone? Someday we will know.
I do want to try DIPT again, but at a substantially higher dose, just so that I can experience what it's like to have my sense of hearing twisted beyond recognition. Friends have said that it's one of those things that you need to try once, just so you can see what it's like. My interest in doing this is totally out of curiosity. I don't think I'd ever take DIPT for recreation; it just doesn't seem to be a substantial enough package. But it is worth trying, so that you can see just how funny a psychedelic drug can be.
Experience Reports are the writings and opinions of the individual authors who submit them.
Some of the activities described are dangerous and/or illegal and none are recommended by Erowid.


Hi there!
I'm Jade Abbott, Founder, NLP Researcher, Speaker
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Director @
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