From 9c0e3c51706ddde64a0f7f3ff54b277cc7be81c4 Mon Sep 17 00:00:00 2001
From: John Crepezzi <john.crepezzi@gmail.com>
Date: Fri, 23 Mar 2012 12:19:42 -0400
Subject: [PATCH] Dice's Coefficient

---
 README.md                                |  5 ++
 lib/natural/distance/dice_coefficient.js | 69 ++++++++++++++++++++++++
 lib/natural/index.js                     |  3 +-
 package.json                             |  2 +-
 spec/dice_coefficient_spec.js            | 26 +++++++++
 5 files changed, 103 insertions(+), 2 deletions(-)
 create mode 100644 lib/natural/distance/dice_coefficient.js
 create mode 100644 spec/dice_coefficient_spec.js

diff --git a/README.md b/README.md
index d63405b56..960f534a9 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,11 @@ Output:
     2
     0
 
+And Dice's co-efficient:
+
+    var natural = require('natural');
+    console.log(natural.DiceCoefficient('thing', 'things'));
+
 Stemmers
 --------
 
diff --git a/lib/natural/distance/dice_coefficient.js b/lib/natural/distance/dice_coefficient.js
new file mode 100644
index 000000000..52655d373
--- /dev/null
+++ b/lib/natural/distance/dice_coefficient.js
@@ -0,0 +1,69 @@
+/*
+Copyright (c) 2011, John Crepezzi, Chris Umbel
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+
+// Get all of the pairs of letters for a string
+var letterPairs = function (str) {
+  var numPairs = str.length - 1;
+  var pairs = new Array(numPairs);
+  for (var i = 0; i < numPairs; i++) {
+    pairs[i] = str.substring(i, i + 2);
+  }
+  return pairs;
+};
+
+// Get all of the pairs in all of the words for a string
+var wordLetterPairs = function (str) {
+  var allPairs = [], pairs;
+  var words = str.split(/\s+/);
+  for (var i = 0; i < words.length; i++) {
+    pairs = letterPairs(words[i]);
+    allPairs.push.apply(allPairs, pairs);
+  }
+  return allPairs;
+};
+
+// Perform some sanitization steps
+var sanitize = function (str) {
+  return str.toLowerCase().replace(/^\s+|\s+$/g, '');
+};
+
+// Compare two strings, and spit out a number from 0-1
+var compare = function (str1, str2) {
+  var pairs1 = wordLetterPairs(sanitize(str1));
+  var pairs2 = wordLetterPairs(sanitize(str2));
+  var intersection = 0, union = pairs1.length + pairs2.length;
+  var i, j, pair1, pair2;
+  for (i = 0; i < pairs1.length; i++) {
+    pair1 = pairs1[i];
+    for (j = 0; j < pairs2.length; j++) {
+      pair2 = pairs2[j];
+      if (pair1 == pair2) {
+        intersection ++;
+        delete pairs2[j];
+        break;
+      }
+    }
+  }
+  return 2 * intersection / union;
+};
+
+module.exports = compare;
diff --git a/lib/natural/index.js b/lib/natural/index.js
index 9d3ef1278..90164775c 100644
--- a/lib/natural/index.js
+++ b/lib/natural/index.js
@@ -40,4 +40,5 @@ exports.SentenceAnalyzer = require('./analyzers/sentence_analyzer');
 exports.stopwords = require('./util/stopwords').words;
 exports.NGrams = require('./ngrams/ngrams');
 exports.JaroWinklerDistance = require('./distance/jaro-winkler_distance');
-exports.LevenshteinDistance = require('./distance/levenshtein_distance');
\ No newline at end of file
+exports.LevenshteinDistance = require('./distance/levenshtein_distance');
+exports.DiceCoefficient = require('./distance/dice_coefficient');
diff --git a/package.json b/package.json
index c2f25f525..e6f88e339 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "natural",
-  "description": "General natural language (tokenizing, stemming, classification, inflection, phonetics, tfidf, WordNet, jaro-winkler, Levenshtein distance) facilities for node.",
+  "description": "General natural language (tokenizing, stemming, classification, inflection, phonetics, tfidf, WordNet, jaro-winkler, Levenshtein distance, Dice's Coefficient) facilities for node.",
   "version": "0.1.4",
   "homepage": "https://github.com/NaturalNode/natural",
   "engines": {
diff --git a/spec/dice_coefficient_spec.js b/spec/dice_coefficient_spec.js
new file mode 100644
index 000000000..eea4e87cc
--- /dev/null
+++ b/spec/dice_coefficient_spec.js
@@ -0,0 +1,26 @@
+var dice = require('lib/natural/distance/dice_coefficient');
+
+describe('dice', function () {
+
+  it('should handle exact matches', function () {
+    expect(dice('john', 'john')).toBe(1);
+  });
+
+  it('should handle total mis-matches', function () {
+    expect(dice('john', 'matt')).toBe(0);
+  });
+
+  // Example from http://en.wikipedia.org/wiki/Dice's_coefficient
+  it('should handle a typical case', function () {
+    expect(dice('night', 'nacht')).toBe(0.25);
+  });
+
+  it('should sanitize case', function () {
+    expect(dice('night', 'NIGHT')).toBe(1);
+  });
+
+  it('should sanitize spacing', function () {
+    expect(dice('the   space', 'the space')).toBe(1);
+  });
+
+});