Added unzip function (and helper) as inverse of _.zip per ticket #1015

test/arrays.js

@@ -129,6 +129,15 @@ $(document).ready(function() {
     equal(String(stooges), 'moe,30,true,larry,40,,curly,50,', 'zipped together arrays of different lengths');
   });
 
+  test('unzip', function() {
+    var stoogesZipped = [['moe',30],['larry',40],['curly',50]];
+    var stoogesUnzipped = _.unzip(stoogesZipped);
+    equal(String(stoogesUnzipped), 'moe,larry,curly,30,40,50', 'unzipped pairs');
+
+    var emptyUnzipped = _.unzip([]);
+    equal(String(emptyUnzipped), ',', 'unzipped empty pairs');
+  });
+
   test('object', function() {
     var result = _.object(['moe', 'larry', 'curly'], [30, 40, 50]);
     var shouldBe = {moe: 30, larry: 40, curly: 50};

underscore.js

@@ -499,6 +499,22 @@
     return results;
   };
 
+  // Internal helper function for `_.unzip`.  Builds arrays out of the 
+  // first and second elements.
+  function constructPair(pair, rests) {
+    return [[_.first(pair)].concat(_.first(rests)),
+            [_.first(_.rest(pair))].concat(_.first(_.rest(rests)))];
+  }
+
+  // The inverse operation to `_.zip`.  That is, takes an array of pairs and 
+  // returns an array of the paired elements split into two left and right
+  // element arrays. For example, `_.unzip` given `[['a',1],['b',2],['c',3]]` 
+  // returns the array [['a','b','c'],[1,2,3]].
+  _.unzip = function(pairs) {
+    if (_.isEmpty(pairs)) return [[],[]];
+    return constructPair(_.first(pairs), _.unzip(_.rest(pairs)));
+  };
+
   // Converts lists into objects. Pass either a single array of `[key, value]`
   // pairs, or two parallel arrays of the same length -- one of keys, and one of
   // the corresponding values.