Sort::Key::Top 0.01

Sort::Key::Top is a Perl module that can 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 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;

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];

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
- 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

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

topsort ltopsort ntopsort itopsort utopsort rtopsort rltopsort
rntopsort ritopsort rutopsort

keytopsort lkeytopsort nkeytopsort ikeytopsort ukeytopsort
rkeytopsort rlkeytopsort rnkeytopsort rikeytopsort rukeytopsort