From 0ce386a3a8dfad02c7a3a7aec13407f38b706cf5 Mon Sep 17 00:00:00 2001
From: Sid N <reddy.siddhartha@rocketmail.com>
Date: Sat, 17 Mar 2012 21:40:19 -0400
Subject: [PATCH 1/2] A module to compute the Levenshtien distance.

---
 lib/natural/distance/levenshtein_distance.js | 41 ++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 lib/natural/distance/levenshtein_distance.js

diff --git a/lib/natural/distance/levenshtein_distance.js b/lib/natural/distance/levenshtein_distance.js
new file mode 100644
index 000000000..ab662f74d
--- /dev/null
+++ b/lib/natural/distance/levenshtein_distance.js
@@ -0,0 +1,41 @@
+/*
+ * Compute the Levenshtein distance between two strings.
+ * Algorithm based from Speech and Language Processing - Daniel Jurafsky and James H. Martin.
+ */
+
+function LevenshteinDistance (source, target, options) {
+
+    options = options || {};
+    options.insertion_cost = options.insertion_cost || 1;
+    options.deletion_cost = options.deletion_cost || 1;
+    options.substitution_cost = options.substitution_cost || 2;
+
+    var sourceLength = source.length;
+    var targetLength = target.length;
+    var distanceMatrix = [[0]];
+    for (var row =  1; row <= sourceLength; row++) {
+        distanceMatrix[row] = [];
+        distanceMatrix[row][0] = distanceMatrix[row-1][0] + options.insertion_cost;
+    }
+    for (var column = 1; column <= targetLength; column++) {
+        distanceMatrix[0][column] = distanceMatrix[column-1][0] + options.deletion_cost;
+    }
+
+    for (var row = 1; row <= sourceLength; row++) {
+        for (var column = 1; column <= targetLength; column++) {
+            var costToInsert = distanceMatrix[row-1][column] + options.insertion_cost;
+            var costToDelete = distanceMatrix[row][column-1] + options.deletion_cost;
+
+            var sourceElement = source[row-1];
+            var targetElement = target[column-1];
+            var costToSubstitute = distanceMatrix[row-1][column-1];
+            if (sourceElement !== targetElement) {
+                costToSubstitute = costToSubstitute + options.substitution_cost;
+            }
+            distanceMatrix[row][column] = Math.min(costToInsert, costToDelete, costToSubstitute);
+        }
+    }
+    return distanceMatrix[sourceLength][targetLength];
+}
+
+module.exports = LevenshteinDistance;

From 9002aa49f13a7c2b7a9226b2a42c92702a56fb21 Mon Sep 17 00:00:00 2001
From: Sid N <snallu@wgen.net>
Date: Wed, 21 Mar 2012 22:01:26 -0400
Subject: [PATCH 2/2] Exporting module for Levenshtien Distance.

---
 lib/natural/index.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/natural/index.js b/lib/natural/index.js
index 29402554e..9d3ef1278 100644
--- a/lib/natural/index.js
+++ b/lib/natural/index.js
@@ -39,4 +39,5 @@ exports.TfIdf = require('./tfidf/tfidf');
 exports.SentenceAnalyzer = require('./analyzers/sentence_analyzer');
 exports.stopwords = require('./util/stopwords').words;
 exports.NGrams = require('./ngrams/ngrams');
-exports.JaroWinklerDistance = require('./distance/jaro-winkler_distance');
\ No newline at end of file
+exports.JaroWinklerDistance = require('./distance/jaro-winkler_distance');
+exports.LevenshteinDistance = require('./distance/levenshtein_distance');
\ No newline at end of file