| Current File : //opt/RZperl518/man/man3/List::Util.3 |
.\" Automatically generated by Pod::Man 2.27 (Pod::Simple 3.28)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings. \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote. \*(C+ will
.\" give a nicer C++. Capital omega is used to do unbreakable dashes and
.\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff,
.\" nothing in troff, for use with C<>.
.tr \(*W-
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
. ds -- \(*W-
. ds PI pi
. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
. if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
. ds L" ""
. ds R" ""
. ds C` ""
. ds C' ""
'br\}
.el\{\
. ds -- \|\(em\|
. ds PI \(*p
. ds L" ``
. ds R" ''
. ds C`
. ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.\"
.\" If the F register is turned on, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD. Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{
. if \nF \{
. de IX
. tm Index:\\$1\t\\n%\t"\\$2"
..
. if !\nF==2 \{
. nr % 0
. nr F 2
. \}
. \}
.\}
.rr rF
.\"
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
.\" Fear. Run. Save yourself. No user-serviceable parts.
. \" fudge factors for nroff and troff
.if n \{\
. ds #H 0
. ds #V .8m
. ds #F .3m
. ds #[ \f1
. ds #] \fP
.\}
.if t \{\
. ds #H ((1u-(\\\\n(.fu%2u))*.13m)
. ds #V .6m
. ds #F 0
. ds #[ \&
. ds #] \&
.\}
. \" simple accents for nroff and troff
.if n \{\
. ds ' \&
. ds ` \&
. ds ^ \&
. ds , \&
. ds ~ ~
. ds /
.\}
.if t \{\
. ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
. ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
. ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
. ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
. ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
. ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
.\}
. \" troff and (daisy-wheel) nroff accents
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
.ds ae a\h'-(\w'a'u*4/10)'e
.ds Ae A\h'-(\w'A'u*4/10)'E
. \" corrections for vroff
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
. \" for low resolution devices (crt and lpr)
.if \n(.H>23 .if \n(.V>19 \
\{\
. ds : e
. ds 8 ss
. ds o a
. ds d- d\h'-1'\(ga
. ds D- D\h'-1'\(hy
. ds th \o'bp'
. ds Th \o'LP'
. ds ae ae
. ds Ae AE
.\}
.rm #[ #] #H #V #F C
.\" ========================================================================
.\"
.IX Title "List::Util 3"
.TH List::Util 3 "2014-10-01" "perl v5.18.4" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.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 LIST\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 \*(AqA\*(Aq..\*(AqZ\*(Aq # \*(AqZ\*(Aq
\& $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 } \*(AqA\*(Aq..\*(AqZ\*(Aq
.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 \*(AqA\*(Aq..\*(AqZ\*(Aq # \*(AqA\*(Aq
\& $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 : $b } \*(AqA\*(Aq..\*(AqZ\*(Aq
.Ve
.IP "reduce \s-1BLOCK LIST\s0" 4
.IX Item "reduce BLOCK LIST"
Reduces \s-1LIST\s0 by calling \s-1BLOCK,\s0 in a scalar context, multiple times,
setting \f(CW$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 } \*(Aqaa\*(Aq..\*(Aqzz\*(Aq # minstr
\& $foo = reduce { $a + $b } 1 .. 10 # sum
\& $foo = reduce { $a . $b } @bar # concat
.Ve
.Sp
If your algorithm requires that \f(CW\*(C`reduce\*(C'\fR produce an identity value, then
make sure that you always pass that identity value as the first argument to prevent
\&\f(CW\*(C`undef\*(C'\fR being returned
.Sp
.Vb 1
\& $foo = reduce { $a + $b } 0, @values; # sum with 0 identity value
.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 If \s-1LIST\s0 is empty then
\&\f(CW\*(C`undef\*(C'\fR is returned.
.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
.Sp
If your algorithm requires that \f(CW\*(C`sum\*(C'\fR produce an identity of 0, then
make sure that you always pass \f(CW0\fR as the first argument to prevent
\&\f(CW\*(C`undef\*(C'\fR being returned
.Sp
.Vb 1
\& $foo = sum 0, @values;
.Ve
.IP "sum0 \s-1LIST\s0" 4
.IX Item "sum0 LIST"
Similar to \f(CW\*(C`sum\*(C'\fR, except this returns 0 when given an empty list, rather
than \f(CW\*(C`undef\*(C'\fR.
.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
\&
\& 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 { $_ } @_ }
\&
\& # How many elements are false
\&
\& sub false { scalar grep { !$_ } @_ }
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Scalar::Util, List::MoreUtils
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 1997\-2007 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.