unixdev.net


Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (OpenBSD-3.6)
Page:
Section:
Apropos / Subsearch:
optional field



ext::List::Util::Perl:Programmeexrts::RLeist::Util::lib::List::Util(3p)


NAME
       List::Util - A selection of general-utility list subrou-
       tines

SYNOPSIS
           use List::Util qw(first max maxstr min minstr reduce shuffle sum);

DESCRIPTION
       "List::Util" contains a selection of subroutines that peo-
       ple 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 numeri-
           cal 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



perl v5.8.5                 2002-11-06                          1





ext::List::Util::Perl:Programmeexrts::RLeist::Util::lib::List::Util(3p)


           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 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, sub-
           sequent 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 con-
           tains one element then that element is returned and
           BLOCK is not executed.





perl v5.8.5                 2002-11-06                          2





ext::List::Util::Perl:Programmeexrts::RLeist::Util::lib::List::Util(3p)


               $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.

               $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




perl v5.8.5                 2002-11-06                          3





ext::List::Util::Perl:Programmeexrts::RLeist::Util::lib::List::Util(3p)


         sub false { scalar grep { !$_ } @_ }

COPYRIGHT
       Copyright (c) 1997-2004 Graham Barr <gbarrATpobox.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                 2002-11-06                          4