build in functionality to at, add string support, optimize, and add more tests

Former-commit-id: 951ef27e55fff5a70d09916b55b85f9e725f751a

lodash.js

@@ -1956,8 +1956,20 @@
    * _.at( ['lodash', 'javascript', 'fast'], 0, 2 );
    * // => ['lodash, 'fast']
    */
-  function at(collection, list) {
+  function at(collection) {
-    return values(pick(collection || [], concat.apply(arguments, slice(arguments, 1))));
+    var index = -1,
+        props = concat.apply(arrayRef, slice(arguments, 1)),
+        length = props.length,
+        result = Array(length);
+
+    if (noCharByIndex && isString(collection)) {
+      collection = collection.split('');
+    }
+
+    while(++index < length) {
+      result[index] = collection[props[index]];
+    }
+    return result;
   }
 
   /**

test/test.js

@@ -681,6 +681,12 @@
     test('no list should return an empty array', function() {
       deepEqual(_.at(['a', 'b', 'c']), [] );
     });
+    test('should work on strings', function() {
+      deepEqual(_.at("helio", [0,3]), ['h', 'i']);
+    });
+    test('should work with multple args', function() {
+      deepEqual(_.at(['a','b','c','d'], 0, 2, 3), ['a', 'c', 'd']);
+    });
   }());
 
   /*--------------------------------------------------------------------------*/