Data::Sorting(3) Multi-key sort using function results


use Data::Sorting qw( :basics :arrays :extras );

# Sorting functions default to simple string comparisons
@names = qw( Bob Alice Ellen Charlie David );
@ordered = sorted_by( undef, @names );

# Various options can be passed before the list values
@ordered = sorted_by( [ -order=>'reverse' ], @names );
# You can also generate a sorting function and then apply it
$function = sort_function();
@ordered = $function->( @names ); # or &{$function}(@names)
@ordered = sort_function( -order=>'reverse' )->( @names );

# The :array functions are prototyped to take the array first
@ordered = sorted_array( @names );
@ordered = sorted_arrayref( \@names );
# You can also sort an array in place, changing its internal order
sort_array( @names );
sort_arrayref( \@names );

# There are several sorting options, such as -compare => 'natural'
@movies = ( 'The Matrix', 'Plan 9', '2001', 'Terminator 2' );
@ordered = sort_function( -compare => 'natural' )->( @movies );
# @ ordered now contains '2001', 'The Matrix', 'Plan 9', 'Terminator 2'

# To sort numbers, pass the -compare => 'numeric' option
@numbers = ( 18, 5, 23, 42, 156, 91, 64 );
@ordered = sorted_by( [ -compare => 'numeric' ], @numbers );
@ordered = sort_function( -compare => 'numeric' )->( @numbers );
@ordered = sorted_array( @numbers, -compare => 'numeric' );
sort_array( @numbers, -compare => 'numeric' );

# You can sort by the results of a function to be called on each item
sort_array( @numbers, -compare => 'numeric', sub { $_[0] % 16 } );
# @numbers now contains 64, 18, 5, 23, 42, 91, 156

# For arrays of datastructures, pass in keys to extract for sorting
@records = (
{ 'rec_id'=>3, 'name'=>{'first'=>'Bob', 'last'=>'Macy'} },
{ 'rec_id'=>1, 'name'=>{'first'=>'Sue', 'last'=>'Jones'} },
{ 'rec_id'=>2, 'name'=>{'first'=>'Al', 'last'=>'Jones' } },
@ordered = sorted_array( @records, 'rec_id' );
# For nested data structures, pass an array of keys to fetch
@ordered = sorted_array( @records, ['name','first'] );
# Pass multiple sort keys for multiple-level sorts
@ordered = sorted_array( @records, ['name','last'], ['name','first'] );

# Any selected sort options are applied to all subsequent sort keys
@ordered = sorted_array( @records,
-order => 'reverse', ['name','last'], ['name','first'] );

# Options specified within a hash-ref apply only to that key
@ordered = sorted_array( @records,
{ order=>'reverse', sortkey=>['name','last'] },
['name','first'] );

# Locale support is available if you have Perl 5.004 or later and POSIX
POSIX::setlocale( POSIX::LC_COLLATE(), 'en_US' );
POSIX::setlocale( POSIX::LC_CTYPE(), 'en_US' );
@ordered = sorted_array( @records,
-compare=>'locale', ['name','last'], ['name','first'] );


Data::Sorting provides functions to sort the contents of arrays based on a collection of extraction and comparison rules. Extraction rules are used to identify the attributes of array elements on which the ordering is based; comparison rules specify how those values should be ordered.

Index strings may be used to retrieve values from array elements, or function references may be passed in to call on each element. Comparison rules are provided for numeric, bytewise, and case-insensitive orders, as well as a 'natural' comparison that places numbers first, in numeric order, followed by the remaining items in case-insensitive textual order.


This module provides several public functions with different calling interfaces that all use the same underlying sorting mechanisms.

These functions may be imported individually or in groups using the following tags:

sorted_by(), sort_function(): General-purpose sorting functions.
sorted_array(), sorted_arrayref(), sort_array(), sort_arrayref(): Prototyped functions for arrays.
sort_key_values(), sort_description(): Two accessory functions that explain how sorting is being carried out.

All of these functions take a list of sorting rules as arguments. See ``Sort Rule Syntax'' for a discussion of the contents of the $sort_rule or @sort_rules parameters shown below.


  @ordered = sorted_by( $sort_rule, @value_array );
  @ordered = sorted_by( $sort_rule, @$value_arrayref );  
  @ordered = sorted_by( $sort_rule, $value1, $value2, $value3 );
  @ordered = sorted_by( \@sort_rules, @value_array );
  @ordered = sorted_by( \@sort_rules, @$value_arrayref );  
  @ordered = sorted_by( \@sort_rules, $value1, $value2, $value3 );

This is a general-purpose sorting function which accepts one or more sort order rules and a list of input values, then returns the values in the order specified by the rules.


  @ordered = sort_function( @sort_rules )->( @value_array );
  @ordered = sort_function( @sort_rules )->( @$value_arrayref );
  @ordered = sort_function( @sort_rules )->( $value1, $value2, $value3 );

Creates an anonymous function which applies the provided sort rules. The function may be cached and used multiple times to apply the same rules again.


  @ordered = sorted_array( @value_array, @sort_rules );
  @ordered = sorted_array( @$value_arrayref, @sort_rules );

Returns a sorted list of the items without altering the order of the original list.


  @ordered = sorted_arrayref( \@value_array, @sort_rules );
  @ordered = sorted_arrayref( $value_arrayref, @sort_rules );

Returns a sorted list of the items without altering the order of the original list.


  sort_array( @value_array, @sort_rules );
  sort_array( @$value_arrayref, @sort_rules );

Sorts the contents of the specified array using a list of sorting rules.


  sort_arrayref( \@value_array, @sort_rules );
  sort_arrayref( $value_arrayref, @sort_rules );

Equivalent to sort_array, but takes an explicit array reference as its first argument, rather than an array variable.


  @key_values = sort_key_values( \@value_array, @sort_rules );
  @key_values = sort_key_values( $value_arrayref, @sort_rules );

Doesn't actually perform any sorting. Extracts and returns the values which would be used as sort keys from each item in the array, in their original order.


  @description = sort_description( $descriptor, @sort_rules );

Doesn't actually perform any sorting. Provides descriptive information about the sort rules for diagnostic purposes.

Sort Rule Syntax

The sort rule argument list may contain several different types of parameters, which are parsed identically by all of the public functions described above.

A sort rule definition list may contain any combination of the following argument structures:

If no sort keys are specified, a default sort key is created using the "extract => "self"" option.

  @ordered = sorted_array( @names );
Specifies a sort key. Each sortkey may be either a scalar value, or an array reference. Appropriate values for a sortkey vary depending on which ``extract'' option is being used, and are discussed further below.

  @ordered = sorted_array( @numbers, sub { $_[0] % 8 } );
  @ordered = sorted_array( @records, 'rec_id' );
  @ordered = sorted_array( @records, ['name','first'] );

Any number of sortkeys may be provided:

  @ordered = sorted_array( @records, ['name','last'], 
                                     ['name','first'] );
-sortkey => sortkey
Another way of specifying a sort key is by preceding it with the ``-sortkey'' flag.

  @ordered = sorted_array( @numbers, -sortkey => sub { $_[0] % 8 } );
  @ordered = sorted_array( @records, -sortkey => ['name','last'], 
                                     -sortkey => ['name','first'] );
{ sortkey => sortkey, option => option_value, ... }
Additional options can be specified by passing a reference to a hash containing a sortkey and values for any number of options described in the list below.

  @ordered = sorted_array( @numbers, { sortkey => sub { abs(shift) },
                                       compare => 'numeric',     } );
-option => option_value
Sets a default option for any subsequent sortkeys in the argument list.

  @ordered = sorted_array( @records, -compare => 'numeric', 
                                     -sortkey => sub { abs(shift) });
  @ordered = sorted_array( @records, -compare => 'textual', 
                                     -sortkey => ['name','last'], 
                                     -sortkey => ['name','first'] );

The possible option values are:

Determines the function which will be used to retrieve the sort key value from each item in the input list.
Determines the function which will be used to order the extracted values.
Can be set to ``reverse'' or ``descending'' to invert the sort order. Defaults to ``ascending''.
Determines the underlying sorting algorithm which will be used to implement the sort. Generally left blank, enabling the module to select the best one available.

Each of these options is discussed at further length below.

Extraction Functions

For the extract option, you may specify one of the following option_values:
The default. Based on the sortkey may behave as the 'self', 'key', or 'method' options described below.
Uses the input value as the sort key, unaltered. Typically used when sorting strings or other scalar values.
Allows for indexing in to hash or array references, allowing you to sort a list of arrayrefs based on the nth value in each, or to sort a list of hashrefs based on a given key.

If the sortkey is an array reference, then the keys are looked up sequentially, allowing you to sort on the contents of a nested hash or array structure.

Uses the sortkey as a method name to be called on each list value, enabling you to sort objects by some calculated value.

If the sortkey is an array reference, then the first value is used as the method name and the remaining values as arguments to that method.

You may pass in a reference to a custom extraction function that will be used to retrieve the sort key values for this rule. The function will be called separately for each value in the input list, receiving that current value as an argument.

If the sortkey is an array reference, then the first value is used as the function reference and the remaining values as arguments to be passed after the item value.

    extract => self | method | key     | code    | CODEREF | ...
    sortkey => -    | | key/idx | CODEREF | args

Comparison Functions

For the compare option, you may specify one of the following option_values:
The default comparison, using Perl's default cmp operator.
A numeric comparison using Perl's <=> operator.
A text-oriented comparison that ignores whitespace and capitalization.
A multi-type comparison that places empty values first, then numeric values in numeric order, then non-textual values like punctuation, followed by textual values in text order. The natural ordering also includes moving subsidiary words to the end, eg ``The Book of Verse'' is sorted as ``Book of Verse, The''
locale : $three_way_cmp
Comparator functions which use the POSIX strcoll function for ordering.
lc_locale : $three_way_cmp
A case-insensitive version of the POSIX strcoll ordering.
Like the 'natural' style, this comparison distinguishes between empty and numeric values, but uses the lc_locale function to sort the textual values.
You may pass in a reference to a custom comparison function that will be used to order the sort key values for this rule.

Each of these functions may return a postive, zero, or negative value based on the relationship of the values in the $a and $b positions of the current @ValueSet array. An undefined return indicates that the comparator is unable to provide an ordering for this pair, in which case the choice will fall through to the next comparator in the list; if no comparator specifies an order, they are left in their original order.

Ascending or Descending Order

For the order option, you may specify one of the following option_values:
forward or ascending
The default order, from lower values to higher ones.
reverse or descending
Reverses the ordering dictated by a sort rule.

Sorting Engines

Depending on the specific sorting rules used in a given call, this module automatically selects an internal function that provides an appropriate approach to implementing the sort, called the sort ``engine''.

You can override this selection by setting an ``engine'' option on the first sort key, which can either contain either the name of one of the engines, described below, or a CODEREF with equivalent behavior.

In the common case of sorting raw values with a cmp comparison, the fast-but-simple ``trivial'' engine is used, which simply applies Perl's default sorting.
For a complex multi-key sort the ``orcish'' engine is typically selected.
Used when there's only one sorting key.

You may also set the $PreCalculate package variable to true to force this engine to be selected. Because the sort key values for the list are calculated before entering Perl's sort operation, there's less of a chance of possible re-entry problems due to nested uses of the sort operator, which causes a fatal error in at least some versions of Perl.

Some sorts are handled with the Guttman-Rosler technique, extracting packed keys and using Perl's default sort function, which is substantially faster, but currently only a limited set of simple comparisons can be handled this way. (For more information on packed-default sorting, see or search for ``Guttman-Rosler''.)


This release of Data::Sorting is intended for public review and feedback.

  Name            DSLIP  Description
  --------------  -----  ---------------------------------------------
  ::Sorting       bdpfp  Multi-key sort using function results

Further information and support for this module is available at

Please report bugs or other problems to <[email protected]>.


The following issues have been noted for future improvements:

Convert more types of comparisons to packed-default sorts for speed.

Further investigate the current status of the Sort::Records module.

Add a comparator function for an alpha-numeric-spans sorting model like Sort::Naturally.

Interface to Sort::PolySort for alternate comparator styles, like ``name'' and ``usdate''.

For non-scalar values, compare referents along the lines of Ref::cmpref().

Provide better handling for nested sorts; perhaps throw an exception from the inner instance to the outer, catch and set $PreCalculate, then go back into the loop?

Replace dynamic scoping with object instances for thread safety. May not be necessary given changes in threading models.


Developed By

  M. Simon Cavalletto, [email protected]
  Evolution Softworks,


Copyright 2003 Matthew Cavalletto.

Portions copyright 1996, 1997, 1998, 1999 Evolution Online Systems, Inc.


You may use, modify, and distribute this software under the same terms as Perl.