Added text distance measure: Jaro-Winkler and Levenshtein (edit) dist…

…ances.

lib/natural/distance/jaro-winkler_distance.js

@@ -0,0 +1,65 @@
+/*
+Copyright (c) 2012, Adam Phillabaum
+
+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.
+
+Unless otherwise stated by a specific section of code
+
+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.
+*/
+
+
+// Computes the Jaro distance between two string -- intrepreted from:
+// http://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance
+// s1 is the first string to compare
+// s2 is the second string to compare
+function jaro_distance(s1,s2) {
+    match_window = (Math.floor(Math.max(s1.length,s2.length))/2)-1;
+    matches = Array();
+    m = 0;
+    for (i=0;i<s1.length;i++) {
+        matches[i] = Array();
+        matched = false;    
+        // this for loop is a little brutal
+        for (k=(i<=match_window)? 0 : i - match_window;
+             (k < i+match_window) && k<s2.length && !matched;
+             k++) {
+                if (s1[i] == s2[k]) {
+                    m++;
+                    matched = true;
+                }
+        }
+    }
+    t = 0; // hack for now... this should actually be computed
+    return (1/3)*(m/s1.length + m/s2.length + (m - t)/m)
+}
+
+// Computes the Winkler distance between two string -- intrepreted from:
+// http://en.wikipedia.org/wiki/Jaro%E2%80%93Winkler_distance
+// s1 is the first string to compare
+// s2 is the second string to compare
+// dj is the Jaro Distance (if you've already computed it), leave blank and the method handles it
+function JaroWinklerDistance(s1, s2, dj) {
+    (typeof(dj) == 'undefined')? jaro = jaro_distance(s1,s2) : jaro = dj;
+    p = 0.1; //
+    l=0 // length of the matching prefix
+    while(s1[l] == s2[l] && l <4)
+        l++;
+
+    return jaro + l*p*(1-jaro);
+}
+module.exports = JaroWinklerDistance;

lib/natural/distance/levenshtein_distance.js

@@ -0,0 +1,23 @@
+// This function is licensed under Creative Commons Share Alike V3 - http://en.wikibooks.org/wiki/Wikibooks:Creative_Commons_Attribution-ShareAlike_3.0_Unported_License
+// Computes the Levenshtein distance between two string -- originally found on:
+// http://en.wikibooks.org/wiki/Algorithm_Implementation/Strings/Levenshtein_distance#JavaScript
+// s1 is the first string to compare
+// s2 is the second string to compare
+function LevenshteinDistance(s1, s2) {
+    var d = [0], c = [0]; // two rows of the distance matrix
+    var distance;
+  for(var e=0; s1[e]; e++) // loop through a and reset the 1st distance
+    for(var f=0; s2[++f];) // loop through b and reset the 1st col of the next row
+      distance=
+      d[f]=
+        (e == 0)? // not the first row ?
+        1+Math.min( // then compute the cost of each change
+          d[--f],
+          c[f]-(s1[e-1]==s2[f]),
+          c[++f]=d[f] // and copy the previous row of the distance matrix
+        )
+        : // otherwise
+        f; // init the very first row of the distance matrix
+  return distance;
+}
+module.exports = LevenshteinDistance;

lib/natural/index.js

@@ -39,3 +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.LevenshteinDistance = require('./distance/levenshtein_distance');
+exports.JaroWinklerDistance = require('./distance/jaro-winkler_distance');