52 lines
1.7 KiB
JavaScript
52 lines
1.7 KiB
JavaScript
|
//#region src/array/groupBy.ts
|
||
|
|
/**
|
||
|
|
* Groups the elements of an array based on a provided key-generating function.
|
||
|
|
*
|
||
|
|
* This function takes an array and a function that generates a key from each element. It returns
|
||
|
|
* an object where the keys are the generated keys and the values are arrays of elements that share
|
||
|
|
* the same key.
|
||
|
|
*
|
||
|
|
* @template T - The type of elements in the array.
|
||
|
|
* @template K - The type of keys.
|
||
|
|
* @param {T[]} arr - The array to group.
|
||
|
|
* @param {(item: T, index: number, array: readonly T[]) => K} getKeyFromItem - A function that generates a key from an element, its index, and the array.
|
||
|
|
* @returns {Record<K, T[]>} An object where each key is associated with an array of elements that
|
||
|
|
* share that key.
|
||
|
|
*
|
||
|
|
* @example
|
||
|
|
* const array = [
|
||
|
|
* { category: 'fruit', name: 'apple' },
|
||
|
|
* { category: 'fruit', name: 'banana' },
|
||
|
|
* { category: 'vegetable', name: 'carrot' }
|
||
|
|
* ];
|
||
|
|
* const result = groupBy(array, item => item.category);
|
||
|
|
* // result will be:
|
||
|
|
* // {
|
||
|
|
* // fruit: [
|
||
|
|
* // { category: 'fruit', name: 'apple' },
|
||
|
|
* // { category: 'fruit', name: 'banana' }
|
||
|
|
* // ],
|
||
|
|
* // vegetable: [
|
||
|
|
* // { category: 'vegetable', name: 'carrot' }
|
||
|
|
* // ]
|
||
|
|
* // }
|
||
|
|
*
|
||
|
|
* @example
|
||
|
|
* // Using index parameter
|
||
|
|
* const items = ['a', 'b', 'c', 'd'];
|
||
|
|
* const result = groupBy(items, (item, index) => index % 2 === 0 ? 'even' : 'odd');
|
||
|
|
* // result will be: { even: ['a', 'c'], odd: ['b', 'd'] }
|
||
|
|
*/
|
||
|
|
function groupBy(arr, getKeyFromItem) {
|
||
|
|
const result = {};
|
||
|
|
for (let i = 0; i < arr.length; i++) {
|
||
|
|
const item = arr[i];
|
||
|
|
const key = getKeyFromItem(item, i, arr);
|
||
|
|
if (!Object.hasOwn(result, key)) result[key] = [];
|
||
|
|
result[key].push(item);
|
||
|
|
}
|
||
|
|
return result;
|
||
|
|
}
|
||
|
|
//#endregion
|
||
|
|
export { groupBy };
|