Add mapValues, mapKeys

snippets/mapKeys.md

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+### mapKeys
+
+Creates an object with keys generated by running the provided function for each key and the same values as the provided object.
+
+Use `Object.keys(obj)` to iterate over the object's keys.
+Use `Array.reduce()` to create a new object with the same values and mapped keys using `fn`.
+
+```js
+const mapKeys = (obj, fn) =>
+  Object.keys(obj).reduce((acc,k) => {acc[fn(obj[k], k, obj)] = obj[k]; return acc;},{});
+```
+
+```js
+mapKeys({ 'a': 1, 'b': 2 }, (val, key) => key + val); // { a1: 1, b2: 2 }
+```

snippets/mapValues.md

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+### 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 }
+```