es-toolkit/docs/reference/array/groupBy.md

groupBy

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.

Signature

function groupBy<T, K extends string>(arr: T[], getKeyFromItem: (item: T) => K): Record<K, T[]>;

Parameters

• arr (T[]): The array to group.
• getKeyFromItem ((item: T) => K): A function that generates a key from an element.

Returns

(Record<K, T[]>) An object where each key is associated with an array of elements that share that key.

Examples

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' }
//   ]
// }