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Salvador Fandiño García


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.).

Multikey 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 expresion 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 multikey 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 multikey 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 non exportable register_type subroutine (see below) 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 multikey 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 $_, $_}, qw(foo fo o of oof));
Sort::Key::register_type($name, \&gensubkeys, @subkeystypes)

registers a new datatype named $name defining how to convert it to a multikey.

&gensubkeys should convert the object of type $name passed on $_ to a list of values composing the multikey.

@subkeystypes is the list of types for the generated multikeys.

For instance:

  Sort::Key::register_type Person =>
                 sub { $_->surname,
                       $_->middlename },
                 qw(str str str);

  Sort::Key::register_type Color =>
                 sub { $_->R, $_->G, $_->B },
                 qw(int int int);

Once a datatype has been registered it can be used in the same way as types supported natively, even for defining new types, i.e.:

  Sort::Key::register_type Family =>
                 sub { $_->man, $_->woman },
                 qw(Person Person);


perl sort function, integer, locale.

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

Other interesting Perl sorting modules are Sort::Maker and Sort::Natural.


Copyright (C) 2005, 2006 by Salvador Fandiño, <sfandino@yahoo.com>.

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.