super-utils-plus/dist/array/groupBy.js

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import { isFunction } from '../utils/is';
/**
 * Creates an object composed of keys generated from the results of running each element
 * of collection through iteratee. The corresponding value of each key is an array of
 * elements responsible for generating the key.
 *
 * @param array - The collection to iterate over
 * @param iteratee - The function invoked per iteration or property name to group by
 * @returns The composed aggregate object
 *
 * @example
 * ```ts
 * groupBy([6.1, 4.2, 6.3], Math.floor);
 * // => { '4': [4.2], '6': [6.1, 6.3] }
 *
 * groupBy(['one', 'two', 'three'], 'length');
 * // => { '3': ['one', 'two'], '5': ['three'] }
 * ```
 */
export function groupBy(array, iteratee) {
    if (!array || !array.length) {
        return {};
    }
    const result = {};
    const iterateeFn = isFunction(iteratee)
        ? iteratee
        : (obj) => String(obj[iteratee]);
    for (const element of array) {
        const key = String(iterateeFn(element));
        if (!result[key]) {
            result[key] = [];
        }
        result[key].push(element);
    }
    return result;
}