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

title, tags

title	tags
partition	array,object,intermediate

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 }]]