Java 8 Streams - Get distinct integers from object list as an array

Question

I'm struggling to work out how to get the distinct integers from an object list as an array using Streams.

Consider I have the below class:

public class Person{

    private int age;
    private double height;

    public Person(int age, double height) {
        this.age= age;
        this.height = height;
    }

    public int getAge() {
        return age;
    }

    public double getHeight() {
        return height;
    }
}

Then consider that have a populated list of these objects e.g. List<Person> people.

My question is, how do I use Java streams to extract the distinct ages into a Int array?

What I have so far is:

List<Integer> distinctAge = people.stream().distinct().mapToInt().collect(Collectors.groupingBy(Person::getAge));

Obviously that doesn't compile but I'm hitting a wall as to where to go next.

Once I have this array, I'm planning to grab all the objects from the list which contain the distinct value - I assume this is also possible using Streams?

If you read what you wrote it would be on the lines of, create a stream of people, then find distinct values amongst them, follow with mapping them to Integer and finally collect these as the result. Revisit this thought and see what all you have to rectify, that might help. — Naman
– Naman, Commented Jan 21, 2021 at 4:10

Ryuzaki L · Accepted Answer · 2021-01-20 18:25:21Z

7

You can collect all ages using map and the call distinct for distinct values

Integer[] ages = persons.stream()
            .map(Person::getAge)
            .distinct()
            .toArray(Integer[]::new);

If you want to collect into int[]

int[] ages = persons.stream()
            .mapToInt(Person::getAge)
            .distinct()
            .toArray();

answered Jan 20, 2021 at 18:25

Ryuzaki L

40.4k14 gold badges81 silver badges111 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

alive · Accepted Answer · 2021-01-21 15:17:06Z

2

Better to use Set instead of using distinct as it improve performance.

Set<Integer> ages = persons.stream().map(Person::getAge).collect(Collectors.toSet());

answered Jan 21, 2021 at 15:17

alive

211 bronze badge

Comments

Mohamed Anees A · Accepted Answer · 2021-01-20 19:08:55Z

1

My question is, how do I use Java streams to extract the distinct ages into a Int array?

Once I have this array, I'm planning to grab all the objects from the list which contain the distinct value - I assume this is also possible using Streams?

Paraphrasing this problem,

You need a Map<Integer,List> where key of the map is the age and the value is a List of Person of that particular age.

Map<Integer, List<Person>> agePersonMap =
        people.stream()
            .collect(Collectors.groupingBy(Person::getAge));

answered Jan 20, 2021 at 19:08

Mohamed Anees A

4,6612 gold badges25 silver badges37 bronze badges

Collectives™ on Stack Overflow

Java 8 Streams - Get distinct integers from object list as an array

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related