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countBy

Count the occurrences of each item in an array based on a mapper function.

Signature

typescript
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

javascript
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 }

Released under the MIT License.