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Manual Reference Pages  -  SORT::KEY (3)

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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 <B>much fasterB>) 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:
keysort { CALC_KEY } @array 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.

nkeysort { CALC_KEY } @array 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

rnkeysort { CALC_KEY } @array works as nkeysort, comparing keys in reverse (or descending) numerical order.
ikeysort { CALC_KEY } @array works as keysort but compares the keys as integers (32 bits or more, no checking is performed for overflows).
rikeysort { CALC_KEY } @array works as ikeysort, but in reverse (or descending) order.
ukeysort { CALC_KEY } @array 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;

rukeysort { CALC_KEY } @array works as ukeysort, but in reverse (or descending) order.
keysort_inplace { CALC_KEY } @array
nkeysort_inplace { CALC_KEY } @array
ikeysort_inplace { CALC_KEY } @array
ukeysort_inplace { CALC_KEY } @array
rkeysort_inplace { CALC_KEY } @array
rnkeysort_inplace { CALC_KEY } @array
rikeysort_inplace { CALC_KEY } @array
rukeysort_inplace { CALC_KEY } @array work as the corresponding keysort functions but sorting the array inplace.
rsort @array
nsort @array
rnsort @array
isort @array
risort @array
usort @array
rusort @array
rsort_inplace @array
nsort_inplace @array
rnsort_inplace @array
isort_inplace @array
risort_inplace @array
usort_inplace @array
rusort_inplace @array 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;

multikeysorter(\&genkeys, @types)
multikeysorter_inplace(\&genkeys, @types) 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 Fandinõ, <>.

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.

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perl v5.20.3 SORT::KEY (3) 2014-04-29

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