Java stream - Sort a List to a HashMap of Lists

Question

Let\'s say I have a Dog class.

Inside it I have a Map and one of the values is Breed.

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Answer 1

You can do it with groupingBy.

Assuming that your input is a List, the Map member inside the Dog class is called map, and the Breed is stored for the "Breed" key :

List dogs = ...
Map> map = dogs.stream()
     .collect(Collectors.groupingBy(d -> d.map.get("Breed")));