Travis build: 1337

README.md

@@ -4354,14 +4354,17 @@ get(obj, 'selector.to.val', 'target[0]', 'target[2].a'); // ['val to select', 1,
 
 ### invertKeyValues
 
-Inverts the key-value pairs of an object, without mutating it.
+Inverts the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.
 
-Use `Object.keys()` and `Array.reduce()` to invert the key-value pairs of an object.
+Use `Object.keys()` and `Array.reduce()` to invert the key-value pairs of an object and apply the function provided (if any).
+Omit the second argument, `fn`, to get the inverted keys without applying a function to them.
 
 ```js
-const invertKeyValues = obj =>
+const invertKeyValues = (obj, fn) =>
   Object.keys(obj).reduce((acc, key) => {
-    acc[obj[key]] = key;
+    const val = fn ? fn(obj[key]) : obj[key];
+    acc[val] = acc[val] || [];
+    acc[val].push(key);
     return acc;
   }, {});
 ```
@@ -4370,7 +4373,8 @@ const invertKeyValues = obj =>
 <summary>Examples</summary>
 
 ```js
-invertKeyValues({ name: 'John', age: 20 }); // { 20: 'age', John: 'name' }
+invertKeyValues({ a: 1, b: 2, c: 1 }); // { 1: [ 'a', 'c' ], 2: [ 'b' ] }
+invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value); // { group1: [ 'a', 'c' ], group2: [ 'b' ] }
 ```
 
 </details>