Usage

counting([1, 2, 3, 4], (n) => (n % 2 === 0 ? "even" : "odd")); // { even: 2, odd: 2 }

Installation

CLI

npx atmx add helper counting

Manually

Copy and paste the following method into @/utils/helpers/undefined.ts:

/**
* Counts the occurrences of each unique value returned by the `identity`
* function when applied to each item in the array.
*
* @example
* counting([1, 2, 3, 4], (n) => n % 2 === 0 ? 'even' : 'odd') // { even: 2, odd: 2 }
*/
export function counting<T, TId extends string | number | symbol>(
array: readonly T[],
identity: (item: T) => TId,
): Record<TId, number> {
if (!array) {
return {} as Record<TId, number>;
}
return array.reduce(
(acc, item) => {
  const id = identity(item);
  acc[id] = (acc[id] ?? 0) + 1;
  return acc;
},
{} as Record<TId, number>,
);
}