Add omitBy, pickBy

snippets/omitBy.md

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+### omitBy
+
+Creates an object composed of the properties the given function returns falsey for. The function is invoked with two arguments: (value, key).
+
+Use `Object.keys(obj)` and `Array.filter()`to remove the keys for which `fn` returns a truthy value.
+Use `Array.reduce()` to convert the filtered keys back to an object with the corresponding key-value pairs.
+
+```js
+const omitBy = (obj, fn) =>
+  Object.keys(obj)
+    .filter(k => !fn(obj[k], k))
+    .reduce((acc, key) => ((acc[key] = obj[key]), acc), {});
+```
+
+```js
+omitBy({ a: 1, b: '2', c: 3 }, x => typeof x === 'number'); // { b: '2' }

snippets/pickBy.md

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+### pickBy
+
+Creates an object composed of the properties the given function returns truthy for. The function is invoked with two arguments: (value, key).
+
+Use `Object.keys(obj)` and `Array.filter()`to remove the keys for which `fn` returns a falsey value.
+Use `Array.reduce()` to convert the filtered keys back to an object with the corresponding key-value pairs.
+
+```js
+const pickBy = (obj, fn) =>
+  Object.keys(obj)
+    .filter(k => fn(obj[k], k))
+    .reduce((acc, key) => ((acc[key] = obj[key]), acc), {});
+```
+
+```js
+pickBy({ a: 1, b: '2', c: 3 }, x => typeof x === 'number'); // { 'a': 1, 'c': 3 }
+```