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List::Util(3perl) | Perl Programmers Reference Guide | List::Util(3perl) |
NAME¶
List::Util - A selection of general-utility list subroutinesSYNOPSIS¶
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
$foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @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
$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
$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
$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
$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.
$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
$foo = reduce { $a + $b } 0, @values; # sum with 0 identity value
- 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
$foo = reduce { $a + $b } 1..10
$foo = sum 0, @values;
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::MoreUtilsCOPYRIGHT¶
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.2011-09-19 | perl v5.14.2 |