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List::Util(3)          Perl Programmers Reference Guide          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(1,2) to have in(1,8) 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 LIST
           Similar to "grep" in(1,8) that it evaluates BLOCK setting $_ to each
           element of LIST in(1,8) 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(1,8) @list
               $foo = first { $_ > $value } @list    # first value in(1,8) @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(1,8) @list

       max LIST
           Returns the entry in(1,8) 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(1,8) the list as strings
           and returns the highest string(3,n) 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(1,8) 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(1,8) the list as strings
           and returns the lowest string(3,n) 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 multiple times, setting $a and $b
           each time. The first call will be with $a and $b set(7,n,1 builtins) 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(1,8)
           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(1,8) a random(3,4,6) order

               @cards = shuffle 0..51      # 0..51 in(1,8) a random(3,4,6) order

       sum LIST
           Returns the sum of all the elements in(1,8) 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(1,8) 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) 1997-2004 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.



perl v5.8.5                       2001-09-21                     List::Util(3)