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SortKey-0.2.0
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NAME

SortKey - Reusable sort key generators

SPECIFICATION VERSION

0.1

VERSION

This document describes version 0.2.0 of SortKey (from Perl distribution SortKey), released on 2024-05-15.

SYNOPSIS

Basic use with sort():

use SortKey::Num::length;
my $by_length = SortKey::Num::length::gen_keygen;

my @sorted = sort { $by_length->($a) <=> $by_length->($b) } "food", "foo", "foolish";
# => ('foo', 'food', 'foolish')

Basic use with Sort::Key:

use Sort::Key qw(nkeysort);
use SortKey::Num::length;
my $by_length = SortKey::Num::length::gen_keygen;

# use & prefix to get around prototype restriction
my @sorted = &nkeysort($by_length, "food", "foo", "foolish");
# => ('foo', 'food', 'foolish')

Specifying arguments:

use Sort::Key qw(nkeysort);
use SortKey::Num::pattern_count;
my $by_pattern_count = Sort::Key::Num::pattern_count::gen_keygen(pattern => qr/foo/);
my @sorted = &nkeysort($by_pattern_count, ...);

Specifying comparer on the command-line (for other CLI's):

% customsort -k length ...
% customsort -c pattern_count=pattern,foo ...

DESCRIPTION

EXPERIMENTAL. SPEC MIGHT STILL CHANGE.

Glossary

A sort key generator is a subroutine that accepts an item and converts it to a string/numeric key. The key then can be compared using the standard <=> or cmp operator.

A SortKey::* module is a module that can return a sort key generator.

Writing a SortKey module

package SorKey::Num::pattern_count;

# required. must return a hash (DefHash)
sub meta {
    return +{
        v => 1,
        summary => 'Number of occurrences of a pattern, as sort key',
        args => {
            pattern => {
                schema => 're_from_str*', # Sah schema
                req => 1,
            },
        },
    };
}

sub gen_keygen {
    my %args = @_;

    ...
    return sub {

        # since one of the main usages is with Sort::Key, and Sort::Key does
        # not pass the argument to @_ but sets $_. So a sort key generator
        # subroutine must check if argument is passed and if not then use $_ as
        # the argument.
        my $arg = @_ ? $_[0] : $_;

        # convert $arg to key
        ...
    };
}

1;

Namespace organization

SortKey::Num::* are for modules that return a numeric key generator. Other subnamespaces are for modules that return a string key.

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/SortKey.

SOURCE

Source repository is at https://github.com/perlancar/perl-SortKey.

SEE ALSO

Base specifications

DefHash

Sah

Sorter

Comparer

Previous incarnation

Sort::Sub

Sorter, SortKey, and Comparer are meant to eventually supersede Sort::Sub. The main improvement over Sort::Sub is the split into three kinds of subroutines:

1. sorter

A subroutine that accepts a list of items to sort.

Sorter::* modules are meant to generate sorters.

2. sort key generator

A subroutine that converts an item to a string/numeric key suitable for simple comparison using eq or == during sorting.

SortKey::* modules are meant to generate sort key generators.

3. comparer

A subroutine that compares two items. Can be used in sort() as custom sort block.

Comparer::* modules are meant to generate comparers.

Perl's sort(), as mentioned above, allows us to specify a comparer, but oftentimes it's more efficient to sort by key using key generator, where the keys are often cached. And sometimes due to preprocessing and/or postprocessing it's more suitable to use the more generic sorter interface.

Aside from the above, SortKey also makes Sort::Sub's special arguments reverse and is_ci become ordinary arguments, because they are not always applicable in all situation, especially is_ci.

AUTHOR

perlancar <perlancar@cpan.org>

CONTRIBUTING

To contribute, you can send patches by email/via RT, or send pull requests on GitHub.

Most of the time, you don't need to build the distribution yourself. You can simply modify the code, then test via:

% prove -l

If you want to build the distribution (e.g. to try to install it locally on your system), you can install Dist::Zilla, Dist::Zilla::PluginBundle::Author::PERLANCAR, Pod::Weaver::PluginBundle::Author::PERLANCAR, and sometimes one or two other Dist::Zilla- and/or Pod::Weaver plugins. Any additional steps required beyond that are considered a bug and can be reported to me.

COPYRIGHT AND LICENSE

This software is copyright (c) 2024 by perlancar <perlancar@cpan.org>.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

BUGS

Please report any bugs or feature requests on the bugtracker website https://rt.cpan.org/Public/Dist/Display.html?Name=SortKey

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.