Add mapValues, mapKeys

snippets/mapValues.md

@@ -0,0 +1,19 @@
+### mapValues
+
+Creates an object with the same keys as the provided object and values generated by running the provided function for each value.
+
+Use `Object.keys(obj)` to iterate over the object's keys.
+Use `Array.reduce()` to create a new object with the same keys and mapped values using `fn`.
+
+```js
+const mapValues = (obj, fn) =>
+  Object.keys(obj).reduce((acc,k) => {acc[k] = fn(obj[k], k, obj); return acc;},{});
+```
+
+```js
+const users = {
+  'fred':    { 'user': 'fred',    'age': 40 },
+  'pebbles': { 'user': 'pebbles', 'age': 1 }
+};
+mapValues(users, u => u.age); // { fred: 40, pebbles: 1 }
+```