| # List::Util.pm |
| # |
| # Copyright (c) 1997-2009 Graham Barr <gbarr@pobox.com>. All rights reserved. |
| # This program is free software; you can redistribute it and/or |
| # modify it under the same terms as Perl itself. |
| # |
| # This module is normally only loaded if the XS module is not available |
| |
| package List::Util; |
| |
| use strict; |
| require Exporter; |
| |
| our @ISA = qw(Exporter); |
| our @EXPORT_OK = qw(first min max minstr maxstr reduce sum shuffle); |
| our $VERSION = "1.25"; |
| our $XS_VERSION = $VERSION; |
| $VERSION = eval $VERSION; |
| |
| require XSLoader; |
| XSLoader::load('List::Util', $XS_VERSION); |
| |
| 1; |
| |
| __END__ |
| |
| =head1 NAME |
| |
| List::Util - A selection of general-utility list subroutines |
| |
| =head1 SYNOPSIS |
| |
| use List::Util qw(first max maxstr min minstr reduce shuffle sum); |
| |
| =head1 DESCRIPTION |
| |
| C<List::Util> contains a selection of subroutines that people have |
| expressed would be nice to have in the perl core, but the usage would |
| not really be high enough to warrant the use of a keyword, and the size |
| so small such that being individual extensions would be wasteful. |
| |
| By default C<List::Util> does not export any subroutines. The |
| subroutines defined are |
| |
| =over 4 |
| |
| =item first BLOCK LIST |
| |
| Similar to C<grep> in that it evaluates BLOCK setting C<$_> to each element |
| of LIST in turn. C<first> returns the first element where the result from |
| BLOCK is a true value. If BLOCK never returns true or LIST was empty then |
| C<undef> is returned. |
| |
| $foo = first { defined($_) } @list # first defined value in @list |
| $foo = first { $_ > $value } @list # first value in @list which |
| # is greater than $value |
| |
| This function could be implemented using C<reduce> like this |
| |
| $foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @list |
| |
| for example wanted() could be defined() which would return the first |
| defined value in @list |
| |
| =item max LIST |
| |
| Returns the entry in the list with the highest numerical value. If the |
| list is empty then C<undef> is returned. |
| |
| $foo = max 1..10 # 10 |
| $foo = max 3,9,12 # 12 |
| $foo = max @bar, @baz # whatever |
| |
| This function could be implemented using C<reduce> like this |
| |
| $foo = reduce { $a > $b ? $a : $b } 1..10 |
| |
| =item maxstr LIST |
| |
| Similar to C<max>, but treats all the entries in the list as strings |
| and returns the highest string as defined by the C<gt> operator. |
| If the list is empty then C<undef> is returned. |
| |
| $foo = maxstr 'A'..'Z' # 'Z' |
| $foo = maxstr "hello","world" # "world" |
| $foo = maxstr @bar, @baz # whatever |
| |
| This function could be implemented using C<reduce> like this |
| |
| $foo = reduce { $a gt $b ? $a : $b } 'A'..'Z' |
| |
| =item min LIST |
| |
| Similar to C<max> but returns the entry in the list with the lowest |
| numerical value. If the list is empty then C<undef> is returned. |
| |
| $foo = min 1..10 # 1 |
| $foo = min 3,9,12 # 3 |
| $foo = min @bar, @baz # whatever |
| |
| This function could be implemented using C<reduce> like this |
| |
| $foo = reduce { $a < $b ? $a : $b } 1..10 |
| |
| =item minstr LIST |
| |
| Similar to C<min>, but treats all the entries in the list as strings |
| and returns the lowest string as defined by the C<lt> operator. |
| If the list is empty then C<undef> is returned. |
| |
| $foo = minstr 'A'..'Z' # 'A' |
| $foo = minstr "hello","world" # "hello" |
| $foo = minstr @bar, @baz # whatever |
| |
| This function could be implemented using C<reduce> like this |
| |
| $foo = reduce { $a lt $b ? $a : $b } 'A'..'Z' |
| |
| =item reduce BLOCK LIST |
| |
| Reduces LIST by calling BLOCK, in a scalar context, multiple times, |
| setting C<$a> and C<$b> each time. The first call will be with C<$a> |
| and C<$b> set to the first two elements of the list, subsequent |
| calls will be done by setting C<$a> to the result of the previous |
| call and C<$b> to the next element in the list. |
| |
| Returns the result of the last call to BLOCK. If LIST is empty then |
| C<undef> is returned. If LIST only contains one element then that |
| element is returned and BLOCK is not executed. |
| |
| $foo = reduce { $a < $b ? $a : $b } 1..10 # min |
| $foo = reduce { $a lt $b ? $a : $b } 'aa'..'zz' # minstr |
| $foo = reduce { $a + $b } 1 .. 10 # sum |
| $foo = reduce { $a . $b } @bar # concat |
| |
| If your algorithm requires that C<reduce> produce an identity value, then |
| make sure that you always pass that identity value as the first argument to prevent |
| C<undef> being returned |
| |
| $foo = reduce { $a + $b } 0, @values; # sum with 0 identity value |
| |
| =item shuffle LIST |
| |
| Returns the elements of LIST in a random order |
| |
| @cards = shuffle 0..51 # 0..51 in a random order |
| |
| =item sum LIST |
| |
| Returns the sum of all the elements in LIST. If LIST is empty then |
| C<undef> is returned. |
| |
| $foo = sum 1..10 # 55 |
| $foo = sum 3,9,12 # 24 |
| $foo = sum @bar, @baz # whatever |
| |
| This function could be implemented using C<reduce> like this |
| |
| $foo = reduce { $a + $b } 1..10 |
| |
| If your algorithm requires that C<sum> produce an identity of 0, then |
| make sure that you always pass C<0> as the first argument to prevent |
| C<undef> being returned |
| |
| $foo = sum 0, @values; |
| |
| =back |
| |
| =head1 KNOWN BUGS |
| |
| With perl versions prior to 5.005 there are some cases where reduce |
| will return an incorrect result. This will show up as test 7 of |
| reduce.t failing. |
| |
| =head1 SUGGESTED ADDITIONS |
| |
| The following are additions that have been requested, but I have been reluctant |
| to add due to them being very simple to implement in perl |
| |
| # One argument is true |
| |
| sub any { $_ && return 1 for @_; 0 } |
| |
| # All arguments are true |
| |
| sub all { $_ || return 0 for @_; 1 } |
| |
| # All arguments are false |
| |
| sub none { $_ && return 0 for @_; 1 } |
| |
| # One argument is false |
| |
| sub notall { $_ || return 1 for @_; 0 } |
| |
| # How many elements are true |
| |
| sub true { scalar grep { $_ } @_ } |
| |
| # How many elements are false |
| |
| sub false { scalar grep { !$_ } @_ } |
| |
| =head1 SEE ALSO |
| |
| L<Scalar::Util>, L<List::MoreUtils> |
| |
| =head1 COPYRIGHT |
| |
| Copyright (c) 1997-2007 Graham Barr <gbarr@pobox.com>. All rights reserved. |
| This program is free software; you can redistribute it and/or |
| modify it under the same terms as Perl itself. |
| |
| =cut |