Java Streams – How to group by value and find min and max value of each group?

Question

For my example, having car object and found that min and max price value based on model (group by).

List carsDetails = UserDB.getCarsDetails();
Ma         


        

Answer 1

Here is a very concise solution. It collects all Cars into a SortedSet and thus works without any additional classes.

Map> grouped = carDetails.stream()
        .collect(groupingBy(Car::getMake, toCollection(
                () -> new TreeSet<>(comparingDouble(Car::getPrice)))));

grouped.forEach((make, cars) -> System.out.println(make
        + " cheapest: " + cars.first()
        + " most expensive: " + cars.last()));

A possible downside is performance, as all Cars are collected, not just the current min and max. But unless the data set is very large, I don't think it will be noticeable.