groupBy

groupBy(array, grouper, transform?)

Groups elements in array by the result of calling grouper function on each element, optionally transforming each element with transform, returning an object with keys as group values and values as arrays of elements.

groupBy(
    [1, 2, 3, 4],
    (x) => (x % 2 === 0 ? "even" : "odd"),
    (x) => x * 10,
);
// { odd: [10, 30], even: [20, 40] }