View file File name : Util.pm Content :# 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 sum0 shuffle); our $VERSION = "1.27"; our $XS_VERSION = $VERSION; $VERSION = eval $VERSION; require XSLoader; XSLoader::load('List::Util', $XS_VERSION); sub sum0 { return 0 unless @_; goto ∑ } 1; __END__ =head1 NAME List::Util - A selection of general-utility list subroutines =head1 SYNOPSIS use List::Util qw(first max maxstr min minstr reduce shuffle sum); =head1 DESCRIPTION C<List::Util> contains a selection of subroutines that people have expressed would be nice to have in the perl core, but the usage would not really be high enough to warrant the use of a keyword, and the size so small such that being individual extensions would be wasteful. By default C<List::Util> does not export any subroutines. The subroutines defined are =over 4 =item first BLOCK LIST Similar to C<grep> in that it evaluates BLOCK setting C<$_> 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; =item sum0 LIST Similar to C<sum>, except this returns 0 when given an empty list, rather than C<undef>. =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