import type { Cast } from '../internal/types/assertion.js';
/**
 * Returns an object composed of keys generated from the results of running each element of the array through `fn`.
 * The corresponding value of each key is an array of the elements responsible for generating the key.
 *
 * @param array The array to iterate over.
 * @param fn Prop, Path, a property name or a function that accepts up to three arguments. The groupBy function calls the fn function one time for each element of the array.
 *
 * @example
 * ```typescript
 * const arr1 = [1, 2, 42];
 * const arr2 = [{ v: 1, n: { v: 1 } }, { v: 2, n: { v: 2 } }, { v: 2, n: { v: 3 } }];
 * groupBy(arr1, (value) => value % 2 === 0 ? 'even' : 'odd'); // => { odd: [1], even: [2, 42] }
 * groupBy(arr2, 'v'); // => { 1: [{ v: 1, n: { v: 1 } }], 2: [{ v: 2, n: { v: 2 } }, { v: 2, n: { v: 3 } }] }
 * groupBy(arr2, prop('v')); // => { 1: [{ v: 1, n: { v: 1 } }], 2: [{ v: 2, n: { v: 2 } }, { v: 2, n: { v: 3 } }] }
 * groupBy(arr2, path('n.v')); // => { 1: [{ v: 1, n: { v: 1 } }], 2: [{ v: 2, n: { v: 2 } }], 3: [{ v: 2, n: { v: 3 } }] }
 * ```
 */
declare const groupBy: {
  <const T, const R extends PropertyKey = PropertyKey>(
    array: T[],
    fn: (value: T, index: number, array: T[]) => R,
  ): {
    [P in R]: T[];
  };
  <
    const T,
    const K extends {
      [P in keyof T]: T[P] extends PropertyKey ? P : never;
    }[keyof T],
  >(
    array: T[],
    propertyName: K,
  ): {
    [P in Cast<T[K], PropertyKey>]: T[];
  };
};
export default groupBy;
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