Rename js snippets

snippets/js/s/group-array-elements-based-on-function.md

@@ -0,0 +1,38 @@
+---
+title: Group array elements based on function
+type: snippet
+language: javascript
+tags: [array]
+cover: switzerland-night
+excerpt: Groups elements based on position in the original arrays and combines them using a function.
+dateModified: 2020-11-03T21:46:13+02:00
+---
+
+Creates an array of elements, grouped based on the position in the original arrays and using a function to specify how grouped values should be combined.
+
+- Check if the last argument provided is a function.
+- Use `Math.max()` to get the longest array in the arguments.
+- Use `Array.from()` to create an array with appropriate length and a mapping function to create array of grouped elements.
+- If lengths of the argument arrays vary, `undefined` is used where no value could be found.
+- The function is invoked with the elements of each group.
+
+```js
+const zipWith = (...array) => {
+  const fn =
+    typeof array[array.length - 1] === 'function' ? array.pop() : undefined;
+  return Array.from({ length: Math.max(...array.map(a => a.length)) }, (_, i) =>
+    fn ? fn(...array.map(a => a[i])) : array.map(a => a[i])
+  );
+};
+```
+
+```js
+zipWith([1, 2], [10, 20], [100, 200], (a, b, c) => a + b + c); // [111, 222]
+zipWith(
+  [1, 2, 3],
+  [10, 20],
+  [100, 200],
+  (a, b, c) =>
+    (a != null ? a : 'a') + (b != null ? b : 'b') + (c != null ? c : 'c')
+); // [111, 222, '3bc']
+```