Tests & implementation of Jaro-Winkler distance.

distance.js

@@ -65,5 +65,21 @@ var jaro = function(str1, str2){
   return (1/3) * (matches/len1 + matches/len2 + (matches - transpositions)/matches);
 };
 
+var jarowinkler = function(str1, str2, weight){
+  // do not exceed 0.25 or distance can exceed 1
+  var WEIGHT = weight ? (weight > 0.25 ? 0.25 : weight) : 0.1,
+      prefix = 0,
+      max = Math.max(str1.length, str2.length),
+      jarodist = jaro(str1, str2);
+
+  for (var i=0; i < max && prefix <= 4; i++) {
+    if (str1[i] == str2[i]) { prefix++; }
+    else { break; }
+  }
+  return jarodist + (prefix * WEIGHT * (1 - jarodist));
+};
+
 exports['hamming'] = hamming;
 exports['jaro'] = jaro;
+exports['jarowinkler'] = jarowinkler;
+

test.js

@@ -11,3 +11,20 @@ assert.equal(dist.jaro('dicksonx', 'dixon'), (1/3)*(4/5+4/8+1));
 assert.equal(dist.jaro('martha', 'marhta'), (1/3)*(1+1+5/6));
 assert.equal(dist.jaro('duane', 'dwayne'), (1/3)*(4/6+4/5+1));
 assert.equal(dist.jaro('jones', 'johnson'), (1/3)*(4/5+4/7+1));
+
+// testing jarowinkler
+(function(){
+  var f = function(distance, prefix) {
+    return distance + (prefix * 0.1 * (1 - distance));
+  };
+
+  var test = function(str1, str2, prefix){
+    var d = dist.jaro(str1, str2);
+    assert.equal(dist.jarowinkler(str1, str2), f(d,prefix));
+  };
+
+  test('dicksonx', 'dixon', 2);
+  test('martha', 'marhta', 3);
+  test('duane', 'dwayne', 1);
+  test('jones', 'johnson', 2);
+})();