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 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 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
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'
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
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 : $b } 'A'..'Z'
Reduces LIST by calling BLOCK multiple times, setting `$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.

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
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 { $_ } @_ }
  # How many elements are false
  sub false { scalar grep { !$_ } @_ }

COPYRIGHT
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.