# mapToDictionary()
Run a dictionary map over the items. The callback should return an associative array with a single key/value pair.
const collection = collect([
{ id: 1, name: 'a' },
{ id: 2, name: 'b' },
{ id: 3, name: 'c' },
{ id: 4, name: 'b' },
]);
const groups = collection.mapToDictionary(item => [item.name, item.id]);
groups.all();
// {
// a: [1],
// b: [2, 4],
// c: [3],
// }