.\" Automatically generated by Pod::Man 2.25 (Pod::Simple 3.16)
.\"
.\" 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" ''
'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.
.ie \nF \{\
.    de IX
.    tm Index:\\$1\t\\n%\t"\\$2"
..
.    nr % 0
.    rr F
.\}
.el \{\
.    de IX
..
.\}
.\"
.\" 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 "Sort::Key::Top 3pm"
.TH Sort::Key::Top 3pm "2011-06-17" "perl v5.14.2" "User Contributed Perl Documentation"
.\" 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"
Sort::Key::Top \- select and sort top n elements
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  use Sort::Key::Top (nkeytop top);
\&
\&  # select 5 first numbers by absolute value:
\&  @top = nkeytop { abs $_ } 5 => 1, 2, 7, 5, 5, 1, 78, 0, \-2, \-8, 2;
\&         # ==> @top = (1, 2, 1, 0, \-2)
\&
\&  # select 5 first numbers by absolute value and sort accordingly:
\&  @top = nkeytopsort { abs $_ } 5 => 1, 2, 7, 5, 5, 1, 78, 0, \-2, \-8, 2;
\&         # ==> @top = (0, 1, 1, 2, \-2)
\&
\&  # select 5 first words by lexicographic order:
\&  @a = qw(cat fish bird leon penguin horse rat elephant squirrel dog);
\&  @top = top 5 => @a;
\&         # ==> @top = qw(cat fish bird elephant dog);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The functions available from this module select the top n elements from a list
using several common orderings and custom key extraction procedures.
.PP
They are all variations around
.PP
.Vb 1
\&  keytopsort { CALC_KEY($_) } $n => @data;
.Ve
.PP
In array context, this function calculates the ordering key for every
element in \f(CW@data\fR using the expression inside the block. Then it
selects and orders the \f(CW$n\fR elements with the lower keys when
compared lexicographically.
.PP
It is equivalent to the pure Perl expression:
.PP
.Vb 1
\&  (sort { CALC_KEY($a) cmp CALC_KEY($b) } @data)[0 .. $n\-1];
.Ve
.PP
If \f(CW$n\fR is negative, the last \f(CW$n\fR elements from the bottom are selected:
.PP
.Vb 2
\&  topsort 3 => qw(foo doom me bar doz hello);
\&       # ==> (\*(Aqbar\*(Aq, \*(Aqdoz\*(Aq, \*(Aqdoom\*(Aq)
\&
\&  topsort \-3 => qw(foo doom me bar doz hello);
\&       # ==> (\*(Aqfoo\*(Aq, \*(Aqhello\*(Aq, \*(Aqme\*(Aq)
\&
\&  top 3 => qw(foo doom me bar doz hello);
\&       # ==> (\*(Aqdoom\*(Aq, \*(Aqbar\*(Aq, \*(Aqdoz\*(Aq)
\&
\&  top \-3 => qw(foo doom me bar doz hello);
\&       # ==> (\*(Aqfoo\*(Aq, \*(Aqme\*(Aq, \*(Aqhello\*(Aq)
.Ve
.PP
In scalar context, the value returned by the functions on this module
is the cutoff value allowing to select nth element from the
array. For instance:
.PP
.Vb 2
\&  # n = 5;
\&  scalar(topsort 5 => @data) eq (sort @data)[4]    # true
\&
\&  # n = \-5;
\&  scalar(topsort \-5 => @data) eq (sort @data)[\-5]  # true
.Ve
.PP
Note that on scalar context, the \f(CW\*(C`sort\*(C'\fR variations (see below) are
usually the right choice:
.PP
.Vb 1
\&  scalar topsort 3 => qw(me foo doz doom me bar hello); # ==> \*(Aqdoz\*(Aq
\&
\&  scalar top 3 => qw(me foo doz doom me bar hello); # ==> \*(Aqbar\*(Aq
.Ve
.PP
Note also, that the index is 1\-based (it starts at one instead of at
zero). The \f(CW\*(C`atpos\*(C'\fR set of functions explained below do the same and
are 0\-based.
.PP
Variations allow to:
.IP "\- use the own values as the ordering keys" 4
.IX Item "- use the own values as the ordering keys"
.Vb 2
\&  topsort 5 => qw(a b ab t uu g h aa aac);
\&     # ==> a aa aac ab b
.Ve
.IP "\- return the selected values in the original order" 4
.IX Item "- return the selected values in the original order"
.Vb 2
\&  top 5 => qw(a b ab t uu g h aa aac);
\&     # ==> a b ab aa aac
.Ve
.IP "\- use a different ordering" 4
.IX Item "- use a different ordering"
For instance comparing the keys as numbers, using the locale
configuration or in reverse order:
.Sp
.Vb 2
\&  rnkeytop { length $_ } 3 => qw(a ab aa aac b t uu g h);
\&     # ==> ab aa aac
\&
\&  rnkeytopsort { length $_ } 3 => qw(a ab aa aac b t uu g h);
\&     # ==> aac ab aa
.Ve
.Sp
A prefix is used to indicate the required ordering:
.RS 4
.IP "(no prefix)" 4
.IX Item "(no prefix)"
lexicographical ascending order
.IP "r" 4
.IX Item "r"
lexicographical descending order
.IP "l" 4
.IX Item "l"
lexicographical ascending order obeying locale configuration
.IP "r" 4
.IX Item "r"
lexicographical descending order obeying locale configuration
.IP "n" 4
.IX Item "n"
numerical ascending order
.IP "rn" 4
.IX Item "rn"
numerical descending order
.IP "i" 4
.IX Item "i"
numerical ascending order but converting the keys to integers first
.IP "ri" 4
.IX Item "ri"
numerical descending order but converting the keys to integers first
.IP "u" 4
.IX Item "u"
numerical ascending order but converting the keys to unsigned integers first
.IP "ru" 4
.IX Item "ru"
numerical descending order but converting the keys to unsigned integers first
.RE
.RS 4
.RE
.IP "\- select the head element from the list sorted" 4
.IX Item "- select the head element from the list sorted"
.Vb 2
\&  nhead 6, 7, 3, 8, 9, 9;
\&      # ==> 3
\&
\&  nkeyhead { length $_ } qw(a ab aa aac b t uu uiyii)
\&      # ==> \*(Aqa\*(Aq
.Ve
.IP "\- select the tail element from the list sorted" 4
.IX Item "- select the tail element from the list sorted"
.Vb 2
\&  tail qw(a ab aa aac b t uu uiyii);
\&      # ==> \*(Aquu\*(Aq
\&
\&  nkeytail { length $_ } qw(a ab aa aac b t uu uiyii)
\&      # ==> \*(Aquiyii\*(Aq
.Ve
.IP "\- select the element at position n from the list sorted" 4
.IX Item "- select the element at position n from the list sorted"
.Vb 2
\&  atpos 3, qw(a ab aa aac b t uu uiyii);
\&      # ==> \*(Aqab\*(Aq;
\&
\&  rnkeyatpos { abs $_ } 2 => \-0.3, 1.1, 4, 0.1, 0.9, \-2;
\&      # ==> 1.1
\&
\&  rnkeyatpos { abs $_ } \-2 => \-0.3, 1.1, 4, 0.1, 0.9, \-2;
\&      # ==> \-0.3
.Ve
.Sp
Note that for the atpos set of functions indexes start at zero.
.IP "\- return a list composed by the elements with the first n ordered keys and then the remaining ones." 4
.IX Item "- return a list composed by the elements with the first n ordered keys and then the remaining ones."
.Vb 2
\&  ikeypart { length $_ } 3 => qw(a bbbb cc ddddd g fd);
\&      # ==> a cc g bbbb ddddd fd
.Ve
.IP "\- return two arrays references, the first array containing the elements with the first n ordered keys and the second with the rest." 4
.IX Item "- return two arrays references, the first array containing the elements with the first n ordered keys and the second with the rest."
.Vb 2
\&  keypartref { length $_ } 3 => qw(a bbbb cc ddddd g fd);
\&      # ==> [a cc g] [bbbb ddddd fd]
.Ve
.PP
The full list of available functions is:
.PP
.Vb 1
\&  top ltop ntop itop utop rtop rltop rntop ritop rutop
\&
\&  keytop lkeytop nkeytop ikeytop ukeytop rkeytop rlkeytop rnkeytop
\&  rikeytop rukeytop
\&
\&  topsort ltopsort ntopsort itopsort utopsort rtopsort rltopsort
\&  rntopsort ritopsort rutopsort
\&
\&  keytopsort lkeytopsort nkeytopsort ikeytopsort ukeytopsort
\&  rkeytopsort rlkeytopsort rnkeytopsort rikeytopsort rukeytopsort
\&
\&  head lhead nhead ihead uhead rhead rlhead rnhead rihead ruhead
\&  keyhead lkeyhead nkeyhead ikeyhead ukeyhead rkeyhead rlkeyhead
\&  rnkeyhead rikeyhead rukeyhead
\&
\&  tail ltail ntail itail utail rtail rltail rntail ritail rutail
\&  keytail lkeytail nkeytail ikeytail ukeytail rkeytail rlkeytail
\&  rnkeytail rikeytail rukeytail
\&
\&  atpos latpos natpos iatpos uatpos ratpos rlatpos rnatpos riatpos
\&  ruatpos keyatpos lkeyatpos nkeyatpos ikeyatpos ukeyatpos rkeyatpos
\&  rlkeyatpos rnkeyatpos rikeyatpos rukeyatpos
\&
\&  part lpart npart ipart upart rpart rlpart rnpart ripart
\&  rupart
\&
\&  keypart lkeypart nkeypart ikeypart ukeypart rkeypart
\&  rlkeypart rnkeypart rikeypart rukeypart
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Sort::Key, \*(L"sort\*(R" in perlfunc.
.PP
The Wikipedia article about selection algorithms
<http://en.wikipedia.org/wiki/Selection_algorithm>.
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
Copyright (C) 2006\-2008, 2011 by Salvador Fandin\*~o
(sfandino@yahoo.com).
.PP
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.8.8 or,
at your option, any later version of Perl 5 you may have available.