| Sort::Key::Top(3pm) | User Contributed Perl Documentation | Sort::Key::Top(3pm) |
Sort::Key::Top - select and sort top n elements
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 $_ } 5 => 1, 2, 7, 5, 5, 1, 78, 0, -2, -8, 2;
# ==> @top = (0, 1, 1, 2, -2)
# select 5 first words by lexicographic order:
@a = qw(cat fish bird leon penguin horse rat elephant squirrel dog);
@top = top 5 => @a;
# ==> @top = qw(cat fish bird elephant dog);
The functions available from this module select the top n elements from a list using several common orderings and custom key extraction procedures.
They are all variations around
keytopsort { CALC_KEY($_) } $n => @data;
In array context, this function calculates the ordering key for every element in @data using the expression inside the block. Then it selects and orders the $n elements with the lower keys when compared lexicographically.
It is equivalent to the pure Perl expression:
(sort { CALC_KEY($a) cmp CALC_KEY($b) } @data)[0 .. $n-1];
If $n is negative, the last $n elements from the bottom are selected:
topsort 3 => qw(foo doom me bar doz hello);
# ==> ('bar', 'doz', 'doom')
topsort -3 => qw(foo doom me bar doz hello);
# ==> ('foo', 'hello', 'me')
top 3 => qw(foo doom me bar doz hello);
# ==> ('doom', 'bar', 'doz')
top -3 => qw(foo doom me bar doz hello);
# ==> ('foo', 'me', 'hello')
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:
# n = 5; scalar(topsort 5 => @data) eq (sort @data)[4] # true # n = -5; scalar(topsort -5 => @data) eq (sort @data)[-5] # true
Note that on scalar context, the "sort" variations (see below) are usually the right choice:
scalar topsort 3 => qw(me foo doz doom me bar hello); # ==> 'doz' scalar top 3 => qw(me foo doz doom me bar hello); # ==> 'bar'
Note also, that the index is 1-based (it starts at one instead of at zero). The "atpos" set of functions explained below do the same and are 0-based.
Variations allow to:
topsort 5 => qw(a b ab t uu g h aa aac);
# ==> a aa aac ab b
slottop 0, 2, [4], [1], [3], [2], [4];
# ==> [1], [2]
top 5 => qw(a b ab t uu g h aa aac);
# ==> a b ab aa aac
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
A prefix is used to indicate the required ordering:
nhead 6, 7, 3, 8, 9, 9;
# ==> 3
nkeyhead { length $_ } qw(a ab aa aac b t uu uiyii)
# ==> 'a'
tail qw(a ab aa aac b t uu uiyii);
# ==> 'uu'
nkeytail { length $_ } qw(a ab aa aac b t uu uiyii)
# ==> 'uiyii'
atpos 3, qw(a ab aa aac b t uu uiyii);
# ==> 'ab';
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
Note that for the "atpos" set of functions indexes start at zero.
ikeypart { length $_ } 3 => qw(a bbbb cc ddddd g fd);
# ==> a cc g bbbb ddddd fd
keypartref { length $_ } 3 => qw(a bbbb cc ddddd g fd);
# ==> [a cc g] [bbbb ddddd fd]
The full list of available functions is:
top ltop ntop itop utop rtop rltop rntop ritop rutop keytop lkeytop nkeytop ikeytop ukeytop rkeytop rlkeytop rnkeytop rikeytop rukeytop slottop lslottop nslottop islottop uslottop rslottop rlslottop rnslottop rislottop ruslottop topsort ltopsort ntopsort itopsort utopsort rtopsort rltopsort rntopsort ritopsort rutopsort keytopsort lkeytopsort nkeytopsort ikeytopsort ukeytopsort rkeytopsort rlkeytopsort rnkeytopsort rikeytopsort rukeytopsort slottopsort lslottopsort nslottopsort islottopsort uslottopsort rslottopsort rlslottopsort rnslottopsort rislottopsort ruslottopsort head lhead nhead ihead uhead rhead rlhead rnhead rihead ruhead keyhead lkeyhead nkeyhead ikeyhead ukeyhead rkeyhead rlkeyhead rnkeyhead rikeyhead rukeyhead slothead lslothead nslothead islothead uslothead rslothead rlslothead rnslothead rislothead ruslothead tail ltail ntail itail utail rtail rltail rntail ritail rutail keytail lkeytail nkeytail ikeytail ukeytail rkeytail rlkeytail rnkeytail rikeytail rukeytail slottail lslottail nslottail islottail uslottail rslottail rlslottail rnslottail rislottail ruslottail atpos latpos natpos iatpos uatpos ratpos rlatpos rnatpos riatpos ruatpos keyatpos lkeyatpos nkeyatpos ikeyatpos ukeyatpos rkeyatpos rlkeyatpos rnkeyatpos rikeyatpos rukeyatpos slotatpos lslotatpos nslotatpos islotatpos uslotatpos rslotatpos rlslotatpos rnslotatpos rislotatpos ruslotatpos part lpart npart ipart upart rpart rlpart rnpart ripart rupart keypart lkeypart nkeypart ikeypart ukeypart rkeypart rlkeypart rnkeypart rikeypart rukeypart slotpart lslotpart nslotpart islotpart uslotpart rslotpart rlslotpart rnslotpart rislotpart ruslotpart
Sort::Key, "sort" in perlfunc.
Sort::Key::Top::PP by Toby Inkster, provides a subset of the API of Sort::Key::Top and is written in pure Perl.
The Wikipedia article about selection algorithms <http://en.wikipedia.org/wiki/Selection_algorithm>.
Copyright (C) 2006-2008, 2011, 2012, 2014 by Salvador Fandiño (sfandino@yahoo.com).
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.
| 2020-11-27 | perl v5.32.0 |