Ensure baseAt uses undefined for non-index values for array-like collections.

lodash.js

@@ -473,26 +473,6 @@
     return false;
   }
 
-  /**
-   * The base implementation of `_.at` without support for strings and individual
-   * key arguments.
-   *
-   * @private
-   * @param {Array|Object} collection The collection to iterate over.
-   * @param {number[]|string[]} [props] The property names or indexes of elements to pick.
-   * @returns {Array} Returns the new array of picked elements.
-   */
-  function baseAt(collection, props) {
-    var index = -1,
-        length = props.length,
-        result = Array(length);
-
-    while(++index < length) {
-      result[index] = collection[props[index]];
-    }
-    return result;
-  }
-
   /**
    * The base implementation of `compareAscending` which compares values and
    * sorts them in ascending order without guaranteeing a stable sort.
@@ -1423,6 +1403,34 @@
       return object;
     }
 
+    /**
+     * The base implementation of `_.at` without support for strings and individual
+     * key arguments.
+     *
+     * @private
+     * @param {Array|Object} collection The collection to iterate over.
+     * @param {number[]|string[]} [props] The property names or indexes of elements to pick.
+     * @returns {Array} Returns the new array of picked elements.
+     */
+    function baseAt(collection, props) {
+      var index = -1,
+          length = collection ? collection.length : 0,
+          isArr = isLength(length),
+          propsLength = props.length,
+          result = Array(propsLength);
+
+      while(++index < propsLength) {
+        var key = props[index];
+        if (isArr) {
+          key = parseFloat(key);
+          result[index] = (key > -1 && key < length && key % 1 == 0) ? collection[key] : undefined;
+        } else {
+          result[index] = collection[key];
+        }
+      }
+      return result;
+    }
+
     /**
      * The base implementation of `_.bindAll` without support for individual
      * method name arguments.