The Collectors.groupingBy Method

//The following example groups members of the collection roster by gender:

	
Map<Person.Sex, List<Person>> byGender =
    roster
        .stream()
        .collect(
            Collectors.groupingBy(Person::getGender));

The groupingBy operation returns a map whose keys are the values that result from applying the lambda expression specified as its parameter (which is called a classification function).

Related concepts

The Collectors.groupingBy Method

The Collectors.groupingBy Method — Structure map

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