countBy

import { countBy } from '@tulx/utils';

/**
 * Creates an object composed of keys generated from the results of running each element of collection thru iteratee.
 * The corresponding value of each key is the number of times the key was returned by iteratee.
 *
 * @param collection - The collection to iterate over.
 * @param iteratee - The iteratee to transform keys.
 * @returns The composed aggregate object.
 *
 * @example
 * ```ts
 * countBy([6.1, 4.2, 6.3], Math.floor); // { '4': 1, '6': 2 }
 * countBy(['one', 'two', 'three'], 'length'); // { '3': 2, '5': 1 }
 * ```
 */
export function countBy<T>(
  collection: readonly T[] | Record<string, T>,
  iteratee: ((value: T) => string | number) | string
): Record<string, number> {
  const getValue =
    typeof iteratee === 'string'
      ? (item: T) => String((item as Record<string, unknown>)[iteratee])
      : (item: T) => String(iteratee(item));

  const result: Record<string, number> = {};

  if (Array.isArray(collection)) {
    const len = collection.length;
    for (let i = 0; i < len; i++) {
      const item = collection[i];
      const key = getValue(item);
      const count = result[key];
      result[key] = count ? count + 1 : 1;
    }
  } else {
    const items = Object.values(collection);
    const len = items.length;
    for (let i = 0; i < len; i++) {
      const item = items[i];
      const key = getValue(item);
      const count = result[key];
      result[key] = count ? count + 1 : 1;
    }
  }

  return result;
}

import { countBy } from '@tulx/utils';

countBy([6.1, 4.2, 6.3], Math.floor); // { '4': 1, '6': 2 }
countBy(['one', 'two', 'three'], 'length'); // { '3': 2, '5': 1 }