Bump to v4.0.0.

invert.js

@@ -0,0 +1,50 @@
+import arrayReduce from './internal/arrayReduce';
+import keys from './keys';
+
+/** Used for built-in method references. */
+var objectProto = Object.prototype;
+
+/** Used to check objects for own properties. */
+var hasOwnProperty = objectProto.hasOwnProperty;
+
+/**
+ * Creates an object composed of the inverted keys and values of `object`.
+ * If `object` contains duplicate values, subsequent values overwrite property
+ * assignments of previous values unless `multiVal` is `true`.
+ *
+ * @static
+ * @memberOf _
+ * @category Object
+ * @param {Object} object The object to invert.
+ * @param {boolean} [multiVal] Allow multiple values per key.
+ * @param- {Object} [guard] Enables use as an iteratee for functions like `_.map`.
+ * @returns {Object} Returns the new inverted object.
+ * @example
+ *
+ * var object = { 'a': 1, 'b': 2, 'c': 1 };
+ *
+ * _.invert(object);
+ * // => { '1': 'c', '2': 'b' }
+ *
+ * // with `multiVal`
+ * _.invert(object, true);
+ * // => { '1': ['a', 'c'], '2': ['b'] }
+ */
+function invert(object, multiVal, guard) {
+  return arrayReduce(keys(object), function(result, key) {
+    var value = object[key];
+    if (multiVal && !guard) {
+      if (hasOwnProperty.call(result, value)) {
+        result[value].push(key);
+      } else {
+        result[value] = [key];
+      }
+    }
+    else {
+      result[value] = key;
+    }
+    return result;
+  }, {});
+}
+
+export default invert;