damerau-levenshtein

The damerau-levenshtein gem allows to find edit distance between two UTF-8 or ASCII encoded strings with O(N**2) efficiency.

This gem implements pure Levenshtein algorithm, Damerau modification of it (where 2 character transposition counts as 1 edit distance). It also includes Boehmer & Rees 2008 modification of Damerau algorithm, where transposition of bigger than 1 character blocks is taken in account as well (Boehmer & Rees 2008).

require 'damerau-levenshtein'
DamerauLevenshtein.distance('Something', 'Smoething') #returns 1

Gem damerau-levenshtein is compatible with ruby versions 1.8.7 and 1.9.2 and higher

Installation

gem install damerau-levenshtein

Examples

require 'rubygems' #not needed for ruby >= 1.9.0
require 'damerau-levenshtein'
dl = DamerauLevenshtein

  • compare using Damerau Levenshtein algorithm

    dl.distance("Something", "Smoething") #returns 1

  • compare using Levensthein algorithm

    dl.distance("Something", "Smoething", 0) #returns 2

  • compare using Boehmer & Rees modification

    dl.distance("Something", "meSothing", 2) #returns 2 instead of 4

  • comparison of words with utf-8 characters should work fine:

    dl.distance("Sjöstedt", "Sjostedt") #returns 1

Description

DamerauLevenshtein.distance takes 4 arguments:

  • string1

  • string2

  • block_size (default is 1)

  • max_distance (default is 10)

block_size determines maximum number of characters in a transposition block:

block_size = 0 (transposition does not count -- it is a pure Levenshtein algorithm)
block_size = 1 (transposition between 2 adjustent characters -- it is pure Damerau-Levenshtein algorithm)
block_size = 2 (transposition between blocks as big as 2 characters -- so abcd and cdab counts as edit distance 2, not 4)
block_size = 3 (transposition between blocks as big as 3 characters -- so abcdef and defabc counts as edit distance 3, not 6)
etc.

max_distance – is a threshold after which algorithm gives up and returns max_distance instead of real edit distance.

Levenshtein algorithm is expensive, so it makes sense to give up when edit distance is becoming too big. The argument max_distance does just that.

DamerauLevenshtein.distance('abcdefg', '1234567', 0, 3) #give up when edit distance exceeds 3)

Contributing to damerau-levenshtein

  • Check out the latest master to make sure the feature hasn’t been implemented or the bug hasn’t been fixed yet

  • Check out the issue tracker to make sure someone already hasn’t requested it and/or contributed it

  • Fork the project

  • Start a feature/bugfix branch

  • Commit and push until you are happy with your contribution

  • Make sure to add tests for it. This is important so I don’t break it in a future version unintentionally.

  • Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

Copyright © 2011 Marine Biological Laboratory. See LICENSE.txt for further details.