Provided by: libsort-key-top-perl_0.08-3_amd64 bug

NAME

       Sort::Key::Top - select and sort top n elements

SYNOPSIS

         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);

DESCRIPTION

       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:

       - use the own values as the ordering keys
             topsort 5 => qw(a b ab t uu g h aa aac);
                # ==> a aa aac ab b

       - use an array or hash index instead of a subroutine to extract the key
             slottop 0, 2, [4], [1], [3], [2], [4];
                # ==> [1], [2]

       - return the selected values in the original order
             top 5 => qw(a b ab t uu g h aa aac);
                # ==> a b ab aa aac

       - use a different ordering
           For instance comparing the keys as numbers, using the locale configuration or in
           reverse order:

             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:

           (no prefix)
               lexicographical ascending order

           r   lexicographical descending order

           l   lexicographical ascending order obeying locale configuration

           r   lexicographical descending order obeying locale configuration

           n   numerical ascending order

           rn  numerical descending order

           i   numerical ascending order but converting the keys to integers first

           ri  numerical descending order but converting the keys to integers first

           u   numerical ascending order but converting the keys to unsigned integers first

           ru  numerical descending order but converting the keys to unsigned integers first

       - select the head element from the list sorted
             nhead 6, 7, 3, 8, 9, 9;
                 # ==> 3

             nkeyhead { length $_ } qw(a ab aa aac b t uu uiyii)
                 # ==> 'a'

       - select the tail element from the list sorted
             tail qw(a ab aa aac b t uu uiyii);
                 # ==> 'uu'

             nkeytail { length $_ } qw(a ab aa aac b t uu uiyii)
                 # ==> 'uiyii'

       - select the element at position n from the list sorted
             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.

       - return a list composed by the elements with the first n ordered keys and then the
       remaining ones.
             ikeypart { length $_ } 3 => qw(a bbbb cc ddddd g fd);
                 # ==> a cc g bbbb ddddd fd

       - return two arrays references, the first array containing the elements with the first n
       ordered keys and the second with the rest.
             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

SEE ALSO

       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 AND LICENSE

       Copyright (C) 2006-2008, 2011, 2012, 2014 by Salvador FandiƱo (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.