Merge remote-tracking branch 'wilkerlucio/simon-similarity'

lib/text/simon_similarity.rb

@@ -0,0 +1,60 @@
+# encoding: utf-8
+#
+# Ruby implementation of the string similarity described by Simon White
+# at: http://www.catalysoft.com/articles/StrikeAMatch.html
+#
+# Based on Java implementation of the article
+#
+# Author: Wilker Lúcio <wilkerlucio@gmail.com>
+#
+
+module Text
+  module SimonSimilarity
+    def compare_strings(str1, str2)
+      pairs1 = word_letter_pairs(str1.upcase)
+      pairs2 = word_letter_pairs(str2.upcase)
+
+      intersection = 0
+      union = pairs1.length + pairs2.length
+
+      pairs1.each do |pair1|
+        pairs2.each_with_index do |pair2, j|
+          if pair1 == pair2
+            intersection += 1
+            pairs2.delete_at(j)
+            break
+          end
+        end
+      end
+
+      (2.0 * intersection) / union
+    end
+
+    private
+
+    def word_letter_pairs(str)
+      pairs = []
+      words = str.split(/\s+/)
+
+      words.each do |word|
+        pairs_in_word = letter_pairs(word)
+        pairs.concat(pairs_in_word)
+      end
+
+      pairs
+    end
+
+    def letter_pairs(str)
+      num_pairs = str.length - 1
+      pairs = []
+
+      0.upto(num_pairs - 1) do |n|
+        pairs << str[n, 2]
+      end
+
+      pairs
+    end
+
+    extend self
+  end
+end

test/test_simon_similarity.rb

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+require File.join(File.dirname(__FILE__), 'preamble')
+require "text/simon_similarity"
+
+class SimonSimilarityTest < Test::Unit::TestCase
+  def test_similarity
+    word = "Healed"
+
+    assert_in_delta 0.8,  Text::SimonSimilarity.compare_strings(word, "Sealed"),  0.01
+    assert_in_delta 0.55, Text::SimonSimilarity.compare_strings(word, "Healthy"), 0.01
+    assert_in_delta 0.44, Text::SimonSimilarity.compare_strings(word, "Heard"),   0.01
+    assert_in_delta 0.40, Text::SimonSimilarity.compare_strings(word, "Herded"),  0.01
+    assert_in_delta 0.25, Text::SimonSimilarity.compare_strings(word, "Help"),    0.01
+    assert_in_delta 0.0,  Text::SimonSimilarity.compare_strings(word, "Sold"),    0.01
+  end
+end