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* [feature/#88] Add countBy.ts * [feature/#88] Add benchmark test of countBy * [feature/#88] Add test code * [feature/#88] Add countBy references * Update docs/ko/reference/array/countBy.md * Apply suggestions from code review --------- Co-authored-by: Sojin Park <raon0211@gmail.com>
735 B
735 B
countBy
Count the occurrences of each item in an array based on a mapper function.
Signature
function countBy<T>(arr: T[], mapper: (item: T) => string): Record<string, number>
Parameters
arr(T[]): The input array to count occurrences.mapper((item: T) => string): The transformation function that maps each item to a string key.
Returns
(Record<string, number>) An object containing the count of each item based on the transformation function.
Examples
import { countBy } from 'es-toolkit/array';
const array = [1, 2, 3, 4, 5, 6];
const result = countBy(array, x => x % 2 === 0 ? 'even' : 'odd');
console.log(result);
// Output: { 'odd': 3, 'even': 3 }