Rename js snippets

snippets/js/s/partition-array.md

@@ -0,0 +1,32 @@
+---
+title: Partition array
+type: snippet
+language: javascript
+tags: [array,object]
+cover: people-on-beach
+dateModified: 2020-10-22T20:24:04+03:00
+---
+
+Applies `fn` to each value in `arr`, splitting it each time the provided function returns a new value.
+
+- Use `Array.prototype.reduce()` with an accumulator object that will hold the resulting array and the last value returned from `fn`.
+- Use `Array.prototype.push()` to add each value in `arr` to the appropriate partition in the accumulator array.
+
+```js
+const partitionBy = (arr, fn) =>
+  arr.reduce(
+    ({ res, last }, v, i, a) => {
+      const next = fn(v, i, a);
+      if (next !== last) res.push([v]);
+      else res[res.length - 1].push(v);
+      return { res, last: next };
+    },
+    { res: [] }
+  ).res;
+```
+
+```js
+const numbers = [1, 1, 3, 3, 4, 5, 5, 5];
+partitionBy(numbers, n => n % 2 === 0); // [[1, 1, 3, 3], [4], [5, 5, 5]]
+partitionBy(numbers, n => n); // [[1, 1], [3, 3], [4], [5, 5, 5]]
+```