list::util(3)

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 de

fined value in @list
$foo = first { $_ > $value } @list # first val

ue 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
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.

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

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