List::Util - A selection of general-utility list subroutines
use List::Util qw(first max maxstr min minstr reduce shuffle sum);
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.
List::Util
By default List::Util does not export any subroutines. The subroutines defined are
Similar 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.
grep
$_
first
undef
$foo = first { defined($_) } @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
reduce
$foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @list
for example wanted() could be defined() which would return the first defined value in @list
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
$foo = reduce { $a > $b ? $a : $b } 1..10
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.
max
gt
$foo = maxstr 'A'..'Z' # 'Z' $foo = maxstr "hello","world" # "world" $foo = maxstr @bar, @baz # whatever
$foo = reduce { $a gt $b ? $a : $b } 'A'..'Z'
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
$foo = reduce { $a < $b ? $a : $b } 1..10
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.
min
lt
$foo = minstr 'A'..'Z' # 'A' $foo = minstr "hello","world" # "hello" $foo = minstr @bar, @baz # whatever
$foo = reduce { $a lt $b ? $a : $b } 'A'..'Z'
Reduces 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.
$a
$b
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
Returns the elements of LIST in a random order
@cards = shuffle 0..51 # 0..51 in a random order
Returns the sum of all the elements in LIST.
$foo = sum 1..10 # 55 $foo = sum 3,9,12 # 24 $foo = sum @bar, @baz # whatever
$foo = reduce { $a + $b } 1..10
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.
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 { $_ } @_ } # How many elements are false sub false { scalar grep { !$_ } @_ }
Copyright (c) 1997-2001 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.
To install if, copy and paste the appropriate command in to your terminal.
cpanm
cpanm if
CPAN shell
perl -MCPAN -e shell install if
For more information on module installation, please visit the detailed CPAN module installation guide.