# # `mapToGroups()`

The mapToGroups method iterates through the collection and passes each value to the given callback:

    const collection = collect([
      { id: 1, name: "A" },
      { id: 2, name: "B" },
      { id: 3, name: "C" },
      { id: 4, name: "B" }
    ]);

    const groups = collection.mapToGroups(function(item, key) {
      return [item.name, item.id];
    });

    //=> {
    //=>   A: [1],
    //=>   B: [2, 4],
    //=>   C: [3],
    //=> }

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