CTAN Comprehensive TeX Archive Network

Directory support/lualibs/lua-uca



The Lua-UCA package


This package adds support for the Unicode collation algorithm for Lua 5.3.


To sort a table using Czech collation rules:

kpse.set_program_name "luatex"
local ducet = require "lua-uca.lua-uca-ducet"
local collator = require "lua-uca.lua-uca-collator"
local languages = require "lua-uca.lua-uca-languages"

local collator_obj = collator.new(ducet)
-- load Czech rules
collator_obj = languages.cs(collator_obj)

local t = {"cihla",  "chochol", "hudba", "jasan", "čáp"}

table.sort(t, function(a,b) 
  return collator_obj:compare_strings(a,b) 

for _, v in ipairs(t) do

The output:

cihla čáp

More samples of the library usage can be found in the source repository of this package on Github. % See HACKING.md file in the repo for more information.

Use with Xindex processor

Xindex is flexible index processor written in Lua by Herbert Voß. It has built-in Lua-UCA support starting with version 0.23. The support can be requested using the -u option:

 xindex -u -l no -c norsk filename.idx

Change sorting rules

The simplest way to change the default sorting order is to use the tailor_string method of the collator_obj object. It updates the collator object using special syntax which is subset of the format used by the Unicode locale data markup language.

collator_obj:tailor_string "&a<b"

Full example with Czech rules:

kpse.set_program_name "luatex"
local ducet = require "lua-uca.lua-uca-ducet"
local collator = require "lua-uca.lua-uca-collator"
local languages = require "lua-uca.lua-uca-languages"

local collator_obj = collator.new(ducet)
local tailoring = function(s) collator_obj:tailor_string(s) end
tailoring "&c<č<<<Č"
tailoring "&h<ch<<<cH<<<Ch<<<CH"
tailoring "&R<ř<<<Ř"
tailoring "&s<š<<<Š"
tailoring "&z<ž<<<Ž"

Note that the sequence of letters ch, Ch, cH and CH will be sorted after h

It is also possible to expand a letter to multiple letters, like this example for DIN 2:

tailoring "&Ö=Oe"
tailoring "&ö=oe"

Some languages, like Norwegian, sort uppercase letters before lowercase. This can be enabled using collator_obj:uppercase_first() function:

local tailoring = function(s) collator_obj:tailor_string(s) end

% More information on a new language support is in the HACKING.md % document in the Lua-UCA Github repo.

Script reordering

Many languages sort different scripts after the script this language uses. As Latin based scripts are sorted first, it is necessary to reorder scripts in such cases.

The collator_obj:reorder function takes table with scripts that need to be reordered. For example Cyrillic can be sorted before Latin using:

collator_obj:reorder {"cyrillic"}

In German or Czech, numbers should be sorted after all other characters. This can be done using:

collator_obj:reorder {"others", "digits"}

The special keyword "others" means that the scripts that follows in the table will be sorted at the very end.

What is missing

  • Algorithm for setting implicit sort weights of characters that are not explicitly listed in DUCET.
  • Special handling of CJK scripts.



Michal Hoftich, 2021. See LICENSE file for more details.


Download the contents of this package in one zip archive (281.3k).

Lua-UCA – Unicode Collation Algorithm library for Lua

The Lua-UCA library provides basic support for Unicode Collation Algorithm in Lua. It can be used to sort arrays of strings according to rules of particular languages. It can be used in other Lua projects that need to sort text in a language dependent way, like indexing processors, bibliographic generators, etc.

Bug trackerhttps://github.com/michal-h21/lua-uca/issues
Version0.1b 2021-11-10
LicensesMIT License
Copyright2020–2021 Michal Hoftich
MaintainerMichal Hoftich
Contained inTeX Live as lua-uca
MiKTeX as lua-uca
Guest Book Sitemap Contact Contact Author