partition.ts

/**
 * @example
 * ```ts
 * const [selectedItems, nonSelectedItems] = partition(array, item => item.selected);
 * const [
 *    numsLessThan5,
 *    numsLessThan10,
 *    numsLessThan30,
 *    numsGreaterEquals30
 *  ] = partition(
 *    numbers,
 *    num => num < 5,
 *    num => num < 10,
 *    num => num < 30,
 * );
 * ```
 */
export const partition = <T>(arr: T[], ...filters: Array<(item: T) => boolean>): T[][] => {
  filters = [...filters, () => true];
  return arr.reduce(
    (partitions, item) => {
      for (let i = 0; i < filters.length; i++) {
        if (filters[i](item)) {
          partitions[i].push(item);
          break;
        }
      }
      return partitions;
    },
    filters.map(() => [] as T[]),
  );
};