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.\" ========================================================================
.\"
.IX Title "List::Util 3"
.TH List::Util 3 "2002-11-24" "perl v5.8.0" "Perl Programmers Reference Guide"
.SH "NAME"
List::Util \- A selection of general\-utility list subroutines
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& use List::Util qw(first max maxstr min minstr reduce shuffle sum);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\f(CW\*(C`List::Util\*(C'\fR 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.
.PP
By default \f(CW\*(C`List::Util\*(C'\fR does not export any subroutines. The
subroutines defined are
.IP "first \s-1BLOCK\s0 \s-1LIST\s0" 4
.IX Item "first BLOCK LIST"
Similar to \f(CW\*(C`grep\*(C'\fR in that it evaluates \s-1BLOCK\s0 setting \f(CW$_\fR to each element
of \s-1LIST\s0 in turn. \f(CW\*(C`first\*(C'\fR returns the first element where the result from
\&\s-1BLOCK\s0 is a true value. If \s-1BLOCK\s0 never returns true or \s-1LIST\s0 was empty then
\&\f(CW\*(C`undef\*(C'\fR is returned.
.Sp
.Vb 3
\& $foo = first { defined($_) } @list # first defined value in @list
\& $foo = first { $_ > $value } @list # first value in @list which
\& # is greater than $value
.Ve
.Sp
This function could be implemented using \f(CW\*(C`reduce\*(C'\fR like this
.Sp
.Vb 1
\& $foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @list
.Ve
.Sp
for example \fIwanted()\fR could be \fIdefined()\fR which would return the first
defined value in \f(CW@list\fR
.IP "max \s-1LIST\s0" 4
.IX Item "max LIST"
Returns the entry in the list with the highest numerical value. If the
list is empty then \f(CW\*(C`undef\*(C'\fR is returned.
.Sp
.Vb 3
\& $foo = max 1..10 # 10
\& $foo = max 3,9,12 # 12
\& $foo = max @bar, @baz # whatever
.Ve
.Sp
This function could be implemented using \f(CW\*(C`reduce\*(C'\fR like this
.Sp
.Vb 1
\& $foo = reduce { $a > $b ? $a : $b } 1..10
.Ve
.IP "maxstr \s-1LIST\s0" 4
.IX Item "maxstr LIST"
Similar to \f(CW\*(C`max\*(C'\fR, but treats all the entries in the list as strings
and returns the highest string as defined by the \f(CW\*(C`gt\*(C'\fR operator.
If the list is empty then \f(CW\*(C`undef\*(C'\fR is returned.
.Sp
.Vb 3
\& $foo = maxstr 'A'..'Z' # 'Z'
\& $foo = maxstr "hello","world" # "world"
\& $foo = maxstr @bar, @baz # whatever
.Ve
.Sp
This function could be implemented using \f(CW\*(C`reduce\*(C'\fR like this
.Sp
.Vb 1
\& $foo = reduce { $a gt $b ? $a : $b } 'A'..'Z'
.Ve
.IP "min \s-1LIST\s0" 4
.IX Item "min LIST"
Similar to \f(CW\*(C`max\*(C'\fR but returns the entry in the list with the lowest
numerical value. If the list is empty then \f(CW\*(C`undef\*(C'\fR is returned.
.Sp
.Vb 3
\& $foo = min 1..10 # 1
\& $foo = min 3,9,12 # 3
\& $foo = min @bar, @baz # whatever
.Ve
.Sp
This function could be implemented using \f(CW\*(C`reduce\*(C'\fR like this
.Sp
.Vb 1
\& $foo = reduce { $a < $b ? $a : $b } 1..10
.Ve
.IP "minstr \s-1LIST\s0" 4
.IX Item "minstr LIST"
Similar to \f(CW\*(C`min\*(C'\fR, but treats all the entries in the list as strings
and returns the lowest string as defined by the \f(CW\*(C`lt\*(C'\fR operator.
If the list is empty then \f(CW\*(C`undef\*(C'\fR is returned.
.Sp
.Vb 3
\& $foo = minstr 'A'..'Z' # 'A'
\& $foo = minstr "hello","world" # "hello"
\& $foo = minstr @bar, @baz # whatever
.Ve
.Sp
This function could be implemented using \f(CW\*(C`reduce\*(C'\fR like this
.Sp
.Vb 1
\& $foo = reduce { $a lt $b ? $a : $b } 'A'..'Z'
.Ve
.IP "reduce \s-1BLOCK\s0 \s-1LIST\s0" 4
.IX Item "reduce BLOCK LIST"
Reduces \s-1LIST\s0 by calling \s-1BLOCK\s0 multiple times, setting \f(CW$a\fR and \f(CW$b\fR
each time. The first call will be with \f(CW$a\fR and \f(CW$b\fR set to the first
two elements of the list, subsequent calls will be done by
setting \f(CW$a\fR to the result of the previous call and \f(CW$b\fR to the next
element in the list.
.Sp
Returns the result of the last call to \s-1BLOCK\s0. If \s-1LIST\s0 is empty then
\&\f(CW\*(C`undef\*(C'\fR is returned. If \s-1LIST\s0 only contains one element then that
element is returned and \s-1BLOCK\s0 is not executed.
.Sp
.Vb 4
\& $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
.Ve
.IP "shuffle \s-1LIST\s0" 4
.IX Item "shuffle LIST"
Returns the elements of \s-1LIST\s0 in a random order
.Sp
.Vb 1
\& @cards = shuffle 0..51 # 0..51 in a random order
.Ve
.IP "sum \s-1LIST\s0" 4
.IX Item "sum LIST"
Returns the sum of all the elements in \s-1LIST\s0.
.Sp
.Vb 3
\& $foo = sum 1..10 # 55
\& $foo = sum 3,9,12 # 24
\& $foo = sum @bar, @baz # whatever
.Ve
.Sp
This function could be implemented using \f(CW\*(C`reduce\*(C'\fR like this
.Sp
.Vb 1
\& $foo = reduce { $a + $b } 1..10
.Ve
.SH "KNOWN BUGS"
.IX Header "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.
.SH "SUGGESTED ADDITIONS"
.IX Header "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
.PP
.Vb 1
\& # One argument is true
.Ve
.PP
.Vb 1
\& sub any { $_ && return 1 for @_; 0 }
.Ve
.PP
.Vb 1
\& # All arguments are true
.Ve
.PP
.Vb 1
\& sub all { $_ || return 0 for @_; 1 }
.Ve
.PP
.Vb 1
\& # All arguments are false
.Ve
.PP
.Vb 1
\& sub none { $_ && return 0 for @_; 1 }
.Ve
.PP
.Vb 1
\& # One argument is false
.Ve
.PP
.Vb 1
\& sub notall { $_ || return 1 for @_; 0 }
.Ve
.PP
.Vb 1
\& # How many elements are true
.Ve
.PP
.Vb 1
\& sub true { scalar grep { $_ } @_ }
.Ve
.PP
.Vb 1
\& # How many elements are false
.Ve
.PP
.Vb 1
\& sub false { scalar grep { !$_ } @_ }
.Ve
.SH "COPYRIGHT"
.IX Header "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.
|
