ext::List::Util::Perl:Programmeexrts::RLeist::Util::lib::List::Util(3p)
List::Util - A selection of general-utility list subroutines
use List::Util qw(first max maxstr min minstr reduce shuffle sum);
"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 indivi-
dual 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
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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, subsequent
calls will be done by setting $a to the result of the
previous call and $b to the next element in the list.
Returns the result of the last call to BLOCK. If LIST is
empty then "undef" is returned. If LIST only contains
one element then that element is returned and BLOCK is
not executed.
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$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
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.
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
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sub true { scalar grep { $_ } @_ }
# How many elements are false
sub false { scalar grep { !$_ } @_ }
Copyright (c) 1997-2005 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.
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