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Partition an array based on a condition

Written byPhuoc Nguyen
13 May, 2020
Last updated
22 Oct, 2021
JavaScript version
const partition = (arr, criteria) => arr.reduce((acc, i) => (acc[criteria(i) ? 0 : 1].push(i), acc), [[], []]);
TypeScript version
const partition = <T,_>(arr: T[], criteria: (a: T) => boolean): T[][] => arr.reduce((acc, i) => (acc[criteria(i) ? 0 : 1].push(i), acc), [[], []]);
partition([1, 2, 3, 4, 5], (n) => n % 2); // [[1, 3, 5], [2, 4]]

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