Rename js snippets

snippets/js/s/function-based-array-element-grouping.md

@@ -0,0 +1,28 @@
+---
+title: Group array elements
+type: snippet
+language: javascript
+tags: [array,object]
+cover: man-cup-laptop
+dateModified: 2020-10-22T20:23:47+03:00
+---
+
+Groups the elements of an array based on the given function.
+
+- Use `Array.prototype.map()` to map the values of the array to a function or property name.
+- Use `Array.prototype.reduce()` to create an object, where the keys are produced from the mapped results.
+
+```js
+const groupBy = (arr, fn) =>
+  arr
+    .map(typeof fn === 'function' ? fn : val => val[fn])
+    .reduce((acc, val, i) => {
+      acc[val] = (acc[val] || []).concat(arr[i]);
+      return acc;
+    }, {});
+```
+
+```js
+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']}
+```