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Sort::Key(3) User Contributed Perl Documentation Sort::Key(3)


Sort::Key - the fastest way to sort anything in Perl


  use Sort::Key qw(keysort nkeysort ikeysort);
  @by_name = keysort { "$_->{surname} $_->{name}" } @people;
  # sorting by a numeric key:
  @by_age = nkeysort { $_->{age} } @people;
  # sorting by a numeric integer key:
  @by_sons = ikeysort { $_->{sons} } @people;


Sort::Key provides a set of functions to sort lists of values by some calculated key value.

It is faster (usually much faster) and uses less memory than other alternatives implemented around perl sort function (ST, GRT, etc.).

Multi-key sorting functionality is also provided via the companion modules Sort::Key::Multi, Sort::Key::Maker and Sort::Key::Register.


This module provides a large number of sorting subroutines but they are all variations off the "keysort" one:

  @sorted = keysort { CALC_KEY($_) } @data

that is conceptually equivalent to

  @sorted = sort { CALC_KEY($a) cmp CALC_KEY($b) } @data

and where CALC_KEY($_) can be any expression to extract the key value from $_ (not only a subroutine call).

For instance, some variations are "nkeysort" that performs a numeric comparison, "rkeysort" that orders the data in descending order, "ikeysort" and "ukeysort" that are optimized versions of "nkeysort" that can be used when the keys are integers or unsigned integers respectively, etc.

Also, inplace versions of the sorters are provided. For instance

  keysort_inplace { CALC_KEY($_) } @data

that is equivalent to

  @data = keysort { CALC_KEY($_) } @data

but being (a bit) faster and using less memory.

The full list of subroutines that can be imported from this module follows:

returns the elements on @array sorted by the key calculated applying "{ CALC_KEY }" to them.

Inside "{ CALC_KEY }", the object is available as $_.

For example:

  @a=({name=>john, surname=>smith}, {name=>paul, surname=>belvedere});
  @by_name=keysort {$_->{name}} @a;

This function honours the "use locale" pragma.

similar to "keysort" but compares the keys numerically instead of as strings.

This function honours the "use integer" pragma, i.e.:

  use integer;
  my @s=(2.4, 2.0, 1.6, 1.2, 0.8);
  my @ns = nkeysort { $_ } @s;
  print "@ns\n"


  0.8 1.6 1.2 2.4 2
works as "nkeysort", comparing keys in reverse (or descending) numerical order.
works as "keysort" but compares the keys as integers (32 bits or more, no checking is performed for overflows).
works as "ikeysort", but in reverse (or descending) order.
works as "keysort" but compares the keys as unsigned integers (32 bits or more).

For instance, it can be used to efficiently sort IP4 addresses:

  my @data = qw(
  my @sorted = ukeysort {
                   my @a = split /\./;
                   (((($a[0] << 8) + $a[1] << 8) + $a[2] << 8) + $a[3])
               } @data;
works as "ukeysort", but in reverse (or descending) order.
work as the corresponding "keysort" functions but sorting the array inplace.
are simplified versions of its "keysort" cousins. They use the own values as the sorting keys.

For instance those constructions are equivalent:

  @sorted = nsort @foo;
  @sorted = nkeysort { $_ } @foo;
  @sorted = sort { $a <=> $b } @foo;
are the low level interface to the multi-key sorting functionality (normally, you should use Sort::Key::Maker and Sort::Key::Register or Sort::Key::Multi instead).

They get a list of keys descriptions and return a reference to a multi-key sorting subroutine.

Types accepted by default are:

  string, str, locale, loc, integer, int,
  unsigned_integer, uint, number, num

and support for additional types can be added via the register_type subroutine available from Sort::Key::Types or the more friendly interface available from Sort::Key::Register.

Types can be preceded by a minus sign to indicate descending order.

If the first argument is a reference to a subroutine it is used as the multi-key extraction function. If not, the generated sorters expect one as their first argument.


  my $sorter1 = multikeysorter(sub {length $_, $_}, qw(int str));
  my @sorted1 = &$sorter1(qw(foo fo o of oof));
  my $sorter2 = multikeysorter(qw(int str));
  my @sorted2 = &$sorter2(sub {length $_, $_}, qw(foo fo o of oof));


perl sort function, integer, locale.

Companion modules Sort::Key::Multi, Sort::Key::Register, Sort::Key::Maker and Sort::Key::Natural.

Sort::Key::IPv4, Sort::Key::DateTime and Sort::Key::OID modules add support for additional datatypes to Sort::Key.

Sort::Key::External allows to sort huge lists that do not fit in the available memory.

Other interesting Perl sorting modules are Sort::Maker, Sort::Naturally and Sort::External.


To report bugs, send me and email or use the CPAN bug tracking system at <>.

Commercial support

Commercial support, professional services and custom software development around this module are available through my current company. Drop me an email with a rough description of your requirements and we will get back to you ASAP.

My wishlist

If you like this module and you're feeling generous, take a look at my Amazon Wish List: <>


Copyright (C) 2005-2007, 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.

2015-04-14 perl v5.38.2