NAME
List::Util - A selection of general-utility list subroutines
SYNOPSIS
use List::Util qw(first max maxstr min minstr reduce shuffle sum);
DESCRIPTION
"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 "List::Util" does not export any subroutines. The subrou-
tines defined are first BLOCK LISTSimilar to "grep" in that it evaluates BLOCK setting $ to each
element of LIST in turn. "first" returns the first element where the result from BLOCK is a true value. If BLOCK never returns true or LIST was empty then "undef" is returned.$foo = first { defined($) } @list # first defined value in @list
$foo = first { $ > $value } @list # first value in @list which
# is greater than $value
This function could be implemented using "reduce" like this$foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @list
for example wanted() could be defined() which would return the first defined value in @list max LIST Returns the entry in the list with the highest numerical value. If the list is empty then "undef" is returned.$foo = max 1..10 # 10
$foo = max 3,9,12 # 12
$foo = max @bar, @baz # whatever
This function could be implemented using "reduce" like this$foo = reduce { $a > $b ? $a : $b } 1..10
maxstr LIST Similar to "max", but treats all the entries in the list as strings and returns the highest string as defined by the "gt" operator. If the list is empty then "undef" is returned.$foo = maxstr 'A'..'Z' # 'Z'
$foo = maxstr "hello","world" # "world"
$foo = maxstr @bar, @baz # whatever
This function could be implemented using "reduce" like this$foo = reduce { $a gt $b ? $a : $b } 'A'..'Z'
min LIST Similar to "max" but returns the entry in the list with the lowest numerical value. If the list is empty then "undef" is returned.$foo = min 1..10 # 1
$foo = min 3,9,12 # 3
$foo = min @bar, @baz # whatever
This function could be implemented using "reduce" like this$foo = reduce { $a < $b ? $a : $b } 1..10
minstr LIST Similar to "min", but treats all the entries in the list as strings and returns the lowest string as defined by the "lt" operator. If the list is empty then "undef" is returned.$foo = minstr 'A'..'Z' # 'A'
$foo = minstr "hello","world" # "hello"
$foo = minstr @bar, @baz # whatever
This function could be implemented using "reduce" like this$foo = reduce { $a lt $b ? $a : $b } 'A'..'Z'
reduce BLOCK LISTReduces LIST by calling BLOCK multiple times, setting $a and $b
each time. The first call will be with $a and $b set to the first
two elements of the list, subsequent calls will be done by setting$a to the result of the previous call and $b to the next element in
the list. Returns the result of the last call to BLOCK. If LIST is empty then "undef" is returned. If LIST only contains one element then that element is returned and BLOCK is not executed.$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 . $b } @bar # concat
shuffle LIST Returns the elements of LIST in a random order@cards = shuffle 0..51 # 0..51 in a random order
sum LIST Returns the sum of all the elements in LIST. If LIST is empty then "undef" is returned.$foo = sum 1..10 # 55
$foo = sum 3,9,12 # 24
$foo = sum @bar, @baz # whatever
This function could be implemented using "reduce" like this$foo = reduce { $a + $b } 1..10
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. SSUUGGGGEESSTTEEDD AADDDDIITTIIOONNSS 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 { !$ } @ }
COPYRIGHTCopyright (c) 1997-2005 Graham Barr
reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.. All rights perl v5.8.8 2001-09-21 List::Util(3pm)