groupBy

The groupBy utility groups array items by a selector function and returns a record of arrays.

Source Code

View Source Code

import type { Primitive } from '../types';

import { assert } from '../function/assert';
import { IS_ARRAY_ERROR_MSG, isArray } from '../typed/isArray';

/**
 * Groups elements by a selector function.
 */
export function groupBy<T>(array: T[], selector: (item: T) => Primitive): Record<string, T[]> {
  assert(isArray(array), IS_ARRAY_ERROR_MSG, { args: { array }, type: TypeError });

  const result: Record<string, T[]> = {};

  for (const item of array) {
    const rawKey = selector(item);
    const key = rawKey === undefined || rawKey === null ? '_' : String(rawKey);

    if (!result[key]) {
      result[key] = [];
    }

    result[key].push(item);
  }

  return result;
}

API

function groupBy<T>(
  array: T[],
  selector: (item: T, index: number, array: T[]) => string | number | boolean,
): Record<string, T[]>;

Example

import { groupBy } from '@vielzeug/toolkit';



const users = [