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-#
-# Levenshtein distance algorithm implementation for Ruby, with UTF-8 support
-#
-# Author:: Paul BATTLEY (pbattley @ gmail.com)
-# Version:: 1.3
-# Date:: 2005-04-19
-#
-# == About
-#
-# The Levenshtein distance is a measure of how similar two strings s and t are,
-# calculated as the number of deletions/insertions/substitutions needed to
-# transform s into t. The greater the distance, the more the strings differ.
-#
-# The Levenshtein distance is also sometimes referred to as the
-# easier-to-pronounce-and-spell 'edit distance'.
-#
-# == Revision history
-#
-# * 2005-05-19 1.3 Repairing an oversight, distance can now be called via
-# Levenshtein.distance(s, t)
-# * 2005-05-04 1.2 Now uses just one 1-dimensional array. I think this is as
-# far as optimisation can go.
-# * 2005-05-04 1.1 Now storing only the current and previous rows of the matrix
-# instead of the whole lot.
-#
-# == Licence
-#
-# Copyright (c) 2005 Paul Battley
-#
-# Usage of the works is permitted provided that this instrument is retained
-# with the works, so that any entity that uses the works is notified of this
-# instrument.
-#
-# DISCLAIMER: THE WORKS ARE WITHOUT WARRANTY.
-#
-
-module Levenshtein
-
- #
- # Calculate the Levenshtein distance between two strings +str1+ and +str2+.
- # +str1+ and +str2+ should be ASCII or UTF-8.
- #
- def distance(str1, str2)
- s = str1.unpack('U*')
- t = str2.unpack('U*')
- n = s.length
- m = t.length
- return m if (0 == n)
- return n if (0 == m)
-
- d = (0..m).to_a
- x = nil
-
- (0...n).each do |i|
- e = i+1
- (0...m).each do |j|
- cost = (s[i] == t[j]) ? 0 : 1
- x = [
- d[j+1] + 1, # insertion
- e + 1, # deletion
- d[j] + cost # substitution
- ].min
- d[j] = e
- e = x
- end
- d[m] = x
- end
-
- return x
- end
-
- extend self
-end
-
-if (__FILE__ == $0)
- require 'test/unit'
-
- class LevenshteinTest < Test::Unit::TestCase
- include Levenshtein
-
- EXPECTED = [
- # Easy ones
- ['test', 'test', 0],
- ['test', 'tent', 1],
- ['gumbo', 'gambol', 2],
- ['kitten', 'sitting', 3],
- # Empty strings
- ['foo', '', 3],
- ['', '', 0],
- ['a', '', 1],
- # UTF-8
- ["f\303\266o", 'foo', 1],
- ["fran\303\247ais", 'francais', 1],
- ["fran\303\247ais", "fran\303\246ais", 1],
- ["\347\247\201\343\201\256\345\220\215\345\211\215\343\201\257"<<
- "\343\203\235\343\203\274\343\203\253\343\201\247\343\201\231",
- "\343\201\274\343\201\217\343\201\256\345\220\215\345\211\215\343\201"<<
- "\257\343\203\235\343\203\274\343\203\253\343\201\247\343\201\231",
- 2], # Japanese
- # Edge cases
- ['a', 'a', 0],
- ['0123456789', 'abcdefghijklmnopqrstuvwxyz', 26]
- ]
-
- def test_known_distances
- EXPECTED.each do |a,b,x|
- assert_equal(x, distance(a, b))
- assert_equal(x, distance(b, a))
- end
- end
- end
-end