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Unicode Collation Algorithm

Unicode::Collate - Unicode Collation Algorithm


Unicode::Collate - Unicode Collation Algorithm


  use Unicode::Collate;


  $Collator = Unicode::Collate->new(%tailoring);


  @sorted = $Collator->sort(@not_sorted);


  $result = $Collator->cmp($a, $b); # returns 1, 0, or -1.


Constructor and Tailoring

The new method returns a collator object.

   $Collator = Unicode::Collate->new(

      alternate => $alternate,

      backwards => $levelNumber, # or \@levelNumbers

      entry => $element,

      normalization  => $normalization_form,

      ignoreName => qr/$ignoreName/,

      ignoreChar => qr/$ignoreChar/,

      katakana_before_hiragana => $bool,

      level => $collationLevel,

      overrideCJK => \&overrideCJK,

      overrideHangul => \&overrideHangul,

      preprocess => \&preprocess,

      rearrange => \@charList,

      table => $filename,

      undefName => qr/$undefName/,

      undefChar => qr/$undefChar/,

      upper_before_lower => $bool,


   # if %tailoring is false (i.e. empty),

   # $Collator should do the default collation.
-- see 3.2.2 Alternate Weighting, UTR #10.

This key allows to alternate weighting for variable collation elements, which are marked with an ASTERISK in the table (NOTE: Many punction marks and symbols are variable in allkeys.txt).

   alternate => 'blanked', 'non-ignorable', 'shifted', or 'shift-trimmed'.

These names are case-insensitive. By default (if specification is omitted), 'shifted' is adopted.

   'Blanked'        Variable elements are ignorable at levels 1 through 3;

                    considered at the 4th level.

   'Non-ignorable'  Variable elements are not reset to ignorable.

   'Shifted'        Variable elements are ignorable at levels 1 through 3

                    their level 4 weight is replaced by the old level 1 weight.

                    Level 4 weight for Non-Variable elements is 0xFFFF.

   'Shift-Trimmed'  Same as 'shifted', but all FFFF's at the 4th level

                    are trimmed.

-- see 3.1.2 French Accents, UTR #10.

     backwards => $levelNumber or \@levelNumbers

Weights in reverse order; ex. level 2 (diacritic ordering) in French. If omitted, forwards at all the levels.

-- see 3.1 Linguistic Features; 3.2.1 File Format, UTR #10.

Overrides a default order or defines additional collation elements

  entry => <<'ENTRIES', # use the UCA file format

00E6 ; [.0861.0020.0002.00E6] [.08B1.0020.0002.00E6] # ligature <ae> as <a><e>

0063 0068 ; [.0893.0020.0002.0063]      # "ch" in traditional Spanish

0043 0068 ; [.0893.0020.0008.0043]      # "Ch" in traditional Spanish


-- see Completely Ignorable, 3.2.2 Alternate Weighting, UTR #10.

Makes the entry in the table ignorable. If a collation element is ignorable, it is ignored as if the element had been deleted from there.

E.g. when 'a' and 'e' are ignorable, 'element' is equal to 'lament' (or 'lmnt').

-- see 4.3 Form a sort key for each string, UTR #10.

Set the maximum level. Any higher levels than the specified one are ignored.

  Level 1: alphabetic ordering

  Level 2: diacritic ordering

  Level 3: case ordering

  Level 4: tie-breaking (e.g. in the case when alternate is 'shifted')

  ex.level => 2,

If omitted, the maximum is the 4th.

-- see 4.1 Normalize each input string, UTR #10.

If specified, strings are normalized before preparation of sort keys (the normalization is executed after preprocess).

As a form name, one of the following names must be used.

  'C'  or 'NFC'  for Normalization Form C

  'D'  or 'NFD'  for Normalization Form D

  'KC' or 'NFKC' for Normalization Form KC

  'KD' or 'NFKD' for Normalization Form KD

If omitted, the string is put into Normalization Form D.

If undef is passed explicitly as the value for this key, any normalization is not carried out (this may make tailoring easier if any normalization is not desired).


-- see 7.1 Derived Collation Elements, UTR #10.

By default, mapping of CJK Unified Ideographs uses the Unicode codepoint order. But the mapping of CJK Unified Ideographs may be overrided.

ex. CJK Unified Ideographs in the JIS code point order.

  overrideCJK => sub {

      my $u = shift;             # get a Unicode codepoint

      my $b = pack('n', $u);     # to UTF-16BE

      my $s = your_unicode_to_sjis_converter($b); # convert

      my $n = unpack('n', $s);   # convert sjis to short

      [ $n, 0x20, 0x2, $u ];     # return the collation element


ex. ignores all CJK Unified Ideographs.

  overrideCJK => sub {()}, # CODEREF returning empty list

   # where ->eq("Pe\x{4E00}rl", "Perl") is true

   # as U+4E00 is a CJK Unified Ideograph and to be ignorable.

If undef is passed explicitly as the value for this key, weights for CJK Unified Ideographs are treated as undefined. But assignment of weight for CJK Unified Ideographs in table or entry is still valid.

-- see 7.1 Derived Collation Elements, UTR #10.

By default, Hangul Syllables are decomposed into Hangul Jamo. But the mapping of Hangul Syllables may be overrided.

This tag works like overrideCJK, so see there for examples.

If you want to override the mapping of Hangul Syllables, the Normalization Forms D and KD are not appropriate (they will be decomposed before overriding).

If undef is passed explicitly as the value for this key, weight for Hangul Syllables is treated as undefined without decomposition into Hangul Jamo. But definition of weight for Hangul Syllables in table or entry is still valid.

-- see 5.1 Preprocessing, UTR #10.

If specified, the coderef is used to preprocess before the formation of sort keys.

ex. dropping English articles, such as ``a'' or ``the''. Then, ``the pen'' is before ``a pencil''.

     preprocess => sub {

           my $str = shift;

           $str =~ s/\b(?:an?|the)\s+//gi;



-- see 3.1.3 Rearrangement, UTR #10.

Characters that are not coded in logical order and to be rearranged. By default,

    rearrange => [ 0x0E40..0x0E44, 0x0EC0..0x0EC4 ],

If you want to disallow any rearrangement, pass undef or [] (a reference to an empty list) as the value for this key.

-- see 3.2 Default Unicode Collation Element Table, UTR #10.

You can use another element table if desired. The table file must be in your lib/Unicode/Collate directory.

By default, the file lib/Unicode/Collate/allkeys.txt is used.

If undef is passed explicitly as the value for this key, no file is read (but you can define collation elements via entry).

A typical way to define a collation element table without any file of table:

   $onlyABC = Unicode::Collate->new(

       table => undef,

       entry => << 'ENTRIES',

0061 ; [.0101.0020.0002.0061] # LATIN SMALL LETTER A

0041 ; [.0101.0020.0008.0041] # LATIN CAPITAL LETTER A

0062 ; [.0102.0020.0002.0062] # LATIN SMALL LETTER B

0042 ; [.0102.0020.0008.0042] # LATIN CAPITAL LETTER B

0063 ; [.0103.0020.0002.0063] # LATIN SMALL LETTER C

0043 ; [.0103.0020.0008.0043] # LATIN CAPITAL LETTER C



-- see 6.3.4 Reducing the Repertoire, UTR #10.

Undefines the collation element as if it were unassigned in the table. This reduces the size of the table. If an unassigned character appears in the string to be collated, the sort key is made from its codepoint as a single-character collation element, as it is greater than any other assigned collation elements (in the codepoint order among the unassigned characters). But, it'd be better to ignore characters unfamiliar to you and maybe never used.

-- see 6.6 Case Comparisons; 7.3.1 Tertiary Weight Table, UTR #10.

By default, lowercase is before uppercase and hiragana is before katakana.

If the tag is made true, this is reversed.

NOTE: These tags simplemindedly assume any lowercase/uppercase or hiragana/katakana distinctions should occur in level 3, and their weights at level 3 should be same as those mentioned in 7.3.1, UTR #10. If you define your collation elements which violates this, these tags doesn't work validly.

Methods for Collation

@sorted = $Collator->sort(@not_sorted)
Sorts a list of strings.

$result = $Collator->cmp($a, $b)
Returns 1 (when $a is greater than $b) or 0 (when $a is equal to $b) or -1 (when $a is lesser than $b).

$result = $Collator->eq($a, $b)
$result = $Collator->ne($a, $b)
$result = $Collator->lt($a, $b)
$result = $Collator->le($a, $b)
$result = $Collator->gt($a, $b)
$result = $Collator->ge($a, $b)
They works like the same name operators as theirs.

   eq : whether $a is equal to $b.

   ne : whether $a is not equal to $b.

   lt : whether $a is lesser than $b.

   le : whether $a is lesser than $b or equal to $b.

   gt : whether $a is greater than $b.

   ge : whether $a is greater than $b or equal to $b.

$sortKey = $Collator->getSortKey($string)
-- see 4.3 Form a sort key for each string, UTR #10.

Returns a sort key.

You compare the sort keys using a binary comparison and get the result of the comparison of the strings using UCA.

   $Collator->getSortKey($a) cmp $Collator->getSortKey($b)

      is equivalent to

   $Collator->cmp($a, $b)

$sortKeyForm = $Collator->viewSortKey($string)
Returns a string formalized to display a sort key. Weights are enclosed with '[' and ']' and level boundaries are denoted by '|'.

   use Unicode::Collate;

   my $c = Unicode::Collate->new();

   print $c->viewSortKey("Perl"),"\n";

    # output:

    # [09B3 08B1 09CB 094F|0020 0020 0020 0020|0008 0002 0002 0002|FFFF FFFF FFFF FFFF]

    #  Level 1             Level 2             Level 3             Level 4

$position = $Collator->index($string, $substring)
($position, $length) = $Collator->index($string, $substring)
-- see 6.8 Searching, UTR #10.

If $substring matches a part of $string, returns the position of the first occurrence of the matching part in scalar context; in list context, returns a two-element list of the position and the length of the matching part.

Notice that the length of the matching part may differ from the length of $substring.

Note that the position and the length are counted on the string after the process of preprocess, normalization, and rearrangement. Therefore, in case the specified string is not binary equal to the preprocessed/normalized/rearranged string, the position and the length may differ form those on the specified string. But it is guaranteed that, if matched, it returns a non-negative value as $position.

If $substring does not match any part of $string, returns -1 in scalar context and an empty list in list context.

e.g. you say

  my $Collator = Unicode::Collate->new( normalization => undef, level => 1 );

  my $str = "Ich mu\x{00DF} studieren.";

  my $sub = "m\x{00FC}ss";

  my $match;

  if (my($pos,$len) = $Collator->index($str, $sub)) {

      $match = substr($str, $pos, $len);


and get "mu\x{00DF}" in $match since "muß" is primary equal to "müss".

Other Methods

Returns the version number of Unicode Technical Standard 10 this module consults.

Returns the version number of the Unicode Standard this module is based on.


None by default.


Unicode::Collate has not been ported to EBCDIC. The code mostly would work just fine but a decision needs to be made: how the module should work in EBCDIC? Should the low 256 characters be understood as Unicode or as EBCDIC code points? Should one be chosen or should there be a way to do either? Or should such translation be left outside the module for the user to do, for example by using Encode::from_to()? (or utf8::unicode_to_native()/utf8::native_to_unicode()?)


Use of the normalization parameter requires the Unicode::Normalize module.

If you need not it (say, in the case when you need not handle any combining characters), assign normalization => undef explicitly.

-- see 6.5 Avoiding Normalization, UTR #10.


index() is an experimental method and its return value may be unreliable. The correct implementation for index() must be based on Locale-Sensitive Support: Level 3 in UTR #18, Unicode Regular Expression Guidelines.

See also 4.2 Locale-Dependent Graphemes in UTR #18.


SADAHIRO Tomoyuki, <>

  Copyright(C) 2001-2002, SADAHIRO Tomoyuki. Japan. All rights reserved.

  This library is free software; you can redistribute it

  and/or modify it under the same terms as Perl itself.

Unicode Collation Algorithm - UTR #10
The Default Unicode Collation Element Table
Unicode Normalization Forms - UAX #15
Unicode Regular Expression Guidelines - UTR #18

the Unicode::Normalize manpage