group by

Tried to reproduce the groupBy behaviour from the lodash lib.
https://lodash.com/docs/4.17.4#groupBy

snippets/group-by

@@ -0,0 +1,16 @@
+### Group by
+
+Passing an array of values, a function or a property name thats going to be run against each value in the array,
+returns an object where the keys are the mapped results and the values is an array of the original values that generated the same results.
+
+```js
+const groupBy = (values, fn) => {
+  return (typeof fn === 'function' ? values.map(fn) : values.map((val) => val[fn]))
+    .reduce((acc, val, i) => {
+      acc[val] = acc[val] === undefined ? [values[i]] : acc[val].concat(values[i]);
+      return acc;
+    }, {});
+}
+// groupBy([6.1, 4.2, 6.3], Math.floor) -> {4: [4.2], 6: [6.1, 6.3]}
+// groupBy(['one', 'two', 'three'], 'length') -> {3: ['one', 'two'], 5: ['three']}
+```