add grab method to get elements in a collection that match the indexes in the provided list array

Former-commit-id: 18df81c229cab4acde8f8157df9bb1001a51e9db

lodash.js

@@ -2175,6 +2175,25 @@
     return collection;
   }
 
+  /**
+   * Grabs the elements in the `collection` using the specified indexes 
+   * in the `list` array.
+   *
+   * @static
+   * @memberOf _
+   * @category Collections
+   * @param {Array|Object|String} collection The collection to iterate over.
+   * @param {Array} list The array of indexes to grab.
+   * @ returns {Array} Returns a new array of elements that matched the list array.
+   * @example
+   *
+   * _.grab( ['a', 'b', 'c', 'd', 'e', 'f'], [0, 2, 5] );
+   * // => ['a', 'c', 'f']
+   */
+  function grab(collection, list) {
+    return invoke(list, function(a){ return a[this]; }, collection);
+  }
+
   /**
    * Creates an object composed of keys returned from running each element of
    * `collection` through a `callback`. The corresponding value of each key is an
@@ -4239,6 +4258,7 @@
   lodash.forIn = forIn;
   lodash.forOwn = forOwn;
   lodash.functions = functions;
+  lodash.grab = grab;
   lodash.groupBy = groupBy;
   lodash.initial = initial;
   lodash.intersection = intersection;

test/test.js

@@ -667,6 +667,28 @@
 
   /*--------------------------------------------------------------------------*/
 
+  QUnit.module('lodash.grab');
+
+  (function() {
+    test('should get items in range', function() {
+      var result = _.grab(['a', 'b',  1.4, 'c',  { 'foo': 'bar' }, 'd'], [0, 2, 4]);
+      deepEqual( result, ['a', 1.4, { 'foo': 'bar' } ]);
+    });
+    test('should work with an object for `collection`', function() {
+      var result = _.grab({ 'a': 'apple', 'b': 'ball', 'c': 'count' }, ['a', 'c']);
+      deepEqual(result, ['apple', 'count']);
+    });
+    test('no list should return an empty array', function() {
+      deepEqual(_.grab(['a', 'b', 'c']), [] );
+    });
+    test('out of range selections should return undefined', function() {
+      var result = _.grab(['a', 'b', 'c'], [1, 9001]);
+      deepEqual( result, ['b', undefined]);
+    });
+  }());
+
+  /*--------------------------------------------------------------------------*/
+
   QUnit.module('lodash.groupBy');
 
   (function() {