Grouping by object value, counting and then setting group key by maximum object attribute

Question

I have managed to write a solution using Java 8 Streams API that first groups a list of object Route by its value and then counts the number of objects in each group. It ret

Answer 1

Here's one approach. First group into lists and then process the lists into the values you actually want:

import static java.util.Comparator.comparingLong;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.toMap;


Map routeCounts = routes.stream()
        .collect(groupingBy(x -> x))
        .values().stream()
        .collect(toMap(
            lst -> lst.stream().max(comparingLong(Route::getLastUpdated)).get(),
            List::size
        ));