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Sort::Key::Natural - fast natural sorting


    use Sort::Key::Natural qw(natsort);

    my @data = qw(foo1 foo23 foo6 bar12 bar1
                  foo bar2 bar-45 foomatic b-a-r-45);

    my @sorted = natsort @data;

    print "@sorted\n";
    # prints:
    #   b-a-r-45 bar1 bar2 bar12 bar-45 foo foo1 foo6 foo23 foomatic

    use Sort::Key::Natural qw(natkeysort);

    my @objects = (...);
    my @sorted = natkeysort { $_->get_id } @objects;


This module extends the Sort::Key family of modules to support natural sorting.

Under natural sorting, strings are split at word and number boundaries, and the resulting substrings are compared as follows:

  • numeric substrings are compared numerically

  • alphabetic substrings are compared lexically

  • numeric substrings come always before alphabetic substrings

Spaces, symbols and non-printable characters are only considered for splitting the string into its parts but not for sorting. For instance foo-bar-42 is broken in three substrings foo, bar and 42 and after that the dashes are ignored.

Note, that the sorting is case sensitive. To do a case insensitive sort you have to convert the keys explicitly:

  my @sorted = natkeysort { lc $_ } @data

Also, once this module is loaded, the new type natural (or nat) will be available from Sort::Key::Maker. For instance:

  use Sort::Key::Natural;
  use Sort::Key::Maker i_rnat_keysort => qw(integer -natural);

creates a multi-key sorter i_rnat_keysort accepting two keys, the first to be compared as an integer and the second in natural descending order.

There is also an alternative set of natural sorting functions that recognize floating point numbers. They use the key type natwf (abbreviation of natural_with_floats).


the functions that can be imported from this module are:

natsort @data

returns the elements of @data sorted in natural order.

rnatsort @data

returns the elements of @data sorted in natural descending order.

natkeysort { CALC_KEY($_) } @data

returns the elements on @array naturally sorted by the keys resulting from applying them CALC_KEY.

rnatkeysort { CALC_KEY($_) } @data

is similar to natkeysort but sorts the elements in descending order.

natsort_inplace @data
rnatsort_inplace @data
natkeysort_inplace { CALC_KEY($_) } @data
rnatkeysort_inplace { CALC_KEY($_) } @data

these functions are similar respectively to natsort, rnatsort, natsortkey and rnatsortkey, but they sort the array @data in place.

$key = mkkey_natural $string

given $string, returns a key that can be compared lexicographically to another key obtained in the same manner, results in the same order as comparing the former strings as in the natural order.

If the argument $key is not provided it defaults to $_.

natwfsort @data
rnatwfsort @data
natwfkeysort { CALC_KEY($_) } @data
rnatwfkeysort { CALC_KEY($_) } @data
natwfsort_inplace @data
rnatwfsort_inplace @data
natwfkeysort_inplace { CALC_KEY($_) } @data
rnatwfkeysort_inplace { CALC_KEY($_) } @data
mkkey_natural_with_floats $key

this ugly named set of functions perform in the same way as its s/natwf/nat/ counterpart with the difference that they honor floating point numbers embedded inside the strings.

In this context a floating point number is a string matching the regular expression /[+\-]?\d+(\.\d*)?/. Note that numbers with an exponent part (i.e. 1.12E-12) are not recognized as such.

Note also that numbers without an integer part (i.e. .2 or -.12) are not supported either.


Sort::Key, Sort::Key::Maker.

Other module providing similar functionality is Sort::Naturally.


Copyright (C) 2006, 2012, 2014 by Salvador Fandiño, <>.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.4 or, at your option, any later version of Perl 5 you may have available.