CODEWITHSUNDEEP
javajava-8java-stream
freitas
freitas

Reputation: 313

Generate lists from a list

I've been searching around and I couldnt find a smart way of doing a split of a list.

Let's say we have the following example:

public class Person {
    private String name;
    private int age;
    private String gender;

    public Person(String name, int age, String gender) {
        this.name = name;
        this.age = age;
        this.gender = gender;
    }

    // Getters/setters
}

So then I have:

List<Person> personList = new ArrayList<>();
personList.add(new Person("Adam", 30, "male"));
personList.add(new Person("John", 32, "male"));
personList.add(new Person("Monica", 30, "female"));
personList.add(new Person("Sophia", 20, "female"));
personList.add(new Person("Carol", 25, "female"));

Is there a way that I could generate two new lists of Person using Stream API grouping male and female?

Upvotes: 2

Views: 147

Answers (2)

J.Adler
J.Adler

Reputation: 1463

Sorry for the brevity, but I'm on the train going home.

Map<String, List<Person>> map = list.stream()
    .collect(Collectors.groupingBy(Person::getGender));

And the code

public class Person {
    private String name;
    private int age;
    private String genre;
 
    public Person(String name, int age, String genre) {
        this.name = name;
        this.age = age;
        this.genre = genre;
    }

    // getters and setters
}

public class GroupBy {

    public static void main(String[] args) {

        List<Person> list = ArrayList();

        list.add(new Person("Adam", 30, male));
        list.add(new Person("John", 32, male));
        list.add(new Person("Monica", 30, female));
        list.add(new Person("Sophia", 20, female));
        list.add(new Person("Carol", 25, female));

        Map<String, List<Person>> map = list.stream()
            .collect(Collectors.groupingBy(Person::getGender));
    }
}

Upvotes: 4

Jacob G.
Jacob G.

Reputation: 29680

If I were you, I'd stream the List and use Collectors.partitioningBy to collect it to a Map<Boolean, List<Person>> where the males are true (or false), and the females are the opposite of the males. It's as simple as the following:

personList.stream()
          .collect(Collectors.partitioningBy(person -> "male".equals(person.getGender())));

Printing this will return the following (after implementing Person#toString):

{false=[Person [Name: Monica, Age: 30, Gender: female], Person [Name: Sophia, Age: 20, Gender: female], Person [Name: Carol, Age: 25, Gender: female]], true=[Person [Name: Adam, Age: 30, Gender: male], Person [Name: John, Age: 32, Gender: male]]}

Upvotes: 4

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