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List::Util(3) User Contributed Perl Documentation List::Util(3)
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 subroutines defined
are
first BLOCK LIST
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.
$foo = first { defined($_) } @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 LIST
Reduces LIST by calling BLOCK, in a scalar context, 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.
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 { $_ } @_ }
# How many elements are false
sub false { scalar grep { !$_ } @_ }
SEE ALSO
Scalar::Util, List::MoreUtils
COPYRIGHT
Copyright (c) 1997-2006 Graham Barr <gbarr AT 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.
perl v5.8.8 2006-12-10 List::Util(3)
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On Apache/1.3.37 (Unix) mod_throttle/3.1.2 FrontPage/5.0.2.2635 mod_psoft_traffic/0.2 mod_ssl/2.8.28 OpenSSL/0.9.8b
Under GNU General Public License
2009-01-07 07:31 @38.103.63.55 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)