group-by.ts

group-by.ts

/**
 * Group array by item into object
 *
 * Polyfill for <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/groupBy>
 * Inspired by <https://stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-an-array-of-objects#answer-64489535>
 */
export const groupBy = <T>(array: Array<T>, predicate: (value: T, index: number, array: Array<T>) => string) =>
  array.reduce(
    (acc, value, index, array) => {
      (acc[predicate(value, index, array)] ||= []).push(value);
      return acc;
    },
    {} as { [key: string]: Array<T> },
  );