30-seconds-of-code/snippets/partition.md

title, tags, expertise, cover, firstSeen, lastUpdated

title	tags	expertise	cover	firstSeen	lastUpdated
Partition array in two	array,object	intermediate	blog_images/sunflowers.jpg	2018-01-08T16:58:23+02:00	2020-11-03T21:46:13+02:00

Groups the elements into two arrays, depending on the provided function's truthiness for each element.

• Use Array.prototype.reduce() to create an array of two arrays.
• Use Array.prototype.push() to add elements for which fn returns true to the first array and elements for which fn returns false to the second one.

const partition = (arr, fn) =>
  arr.reduce(
    (acc, val, i, arr) => {
      acc[fn(val, i, arr) ? 0 : 1].push(val);
      return acc;
    },
    [[], []]
  );

const users = [
  { user: 'barney', age: 36, active: false },
  { user: 'fred', age: 40, active: true },
];
partition(users, o => o.active);
// [
//   [{ user: 'fred', age: 40, active: true }],
//   [{ user: 'barney', age: 36, active: false }]
// ]