Remove duplicate from List java8

Question

I have a class below, and wanted to remove duplicate person which contain same name, how to do by using Java8 Lambda, expected List contains p1, p3 from the below.

Person:

public class Person {

public int id;
public String name;
public String city;

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
}

}

Testing:

import java.util.ArrayList;
import java.util.List;

public class Testing {

public static void main(String[] args) {

    List<Person> persons = new ArrayList<>();

    Person p1 = new Person();
    p1.setId(1);
    p1.setName("Venkat");
    p1.setCity("Bangalore");
    Person p2 = new Person();

    p2.setId(2);
    p2.setName("Venkat");
    p2.setCity("Bangalore");

    Person p3 = new Person();
    p3.setId(3);
    p3.setName("Kumar");
    p3.setCity("Chennai");

    persons.add(p1);
    persons.add(p2);
    persons.add(p3);

}
}

look at https://stackoverflow.com/questions/29670116/remove-duplicates-from-a-list-of-objects-based-on-property-in-java-8 — Adrian, Jul 31 '17 at 14:35
override equals & hashcode methods in Person class for duplication removal using Set — Noman Khan, May 29 '18 at 17:03
https://stackoverflow.com/questions/23699371/java-8-distinct-by-property[enter link description here](https://stackoverflow.com/questions/23699371/java-8-distinct-by-property) — 取一个好的名字, May 09 '19 at 07:30

Eugene · Answer 1 · 2017-07-31T20:14:03.667

35

You could filter them out and generate a unique Set:

Set<Person> set = persons.stream()
            .collect(Collectors.toCollection(() -> 
                 new TreeSet<>(Comparator.comparing(Person::getName))));

Or even nicer:

Set<String> namesAlreadySeen = new HashSet<>();

persons.removeIf(p -> !namesAlreadySeen.add(p.getName()));

edited Jul 31 '17 at 20:14

answered Jul 31 '17 at 14:40

Eugene

110,516
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277

ooh, you faster than me, +1! you should tell the OP to make the `persons` to `List` rather than `List – holi-java Jul 31 '17 at 14:43
4

You actually don't need a stream for this, do you? Just create the `TreeSet` with the comparator and then use `addAll`. – fps Jul 31 '17 at 15:16
1

No need for block syntax here, you can use the compact expression syntax just like [here](https://stackoverflow.com/a/29672489/2711488). – Holger Jul 31 '17 at 17:18
1

@FedericoPeraltaSchaffner you're right, I don't have to use streams... thx – Eugene Jul 31 '17 at 20:14
Helped me with some other kind of problem :p – Majid Ali Khan Nov 26 '19 at 07:29

score 30 · Answer 2 · answered Nov 01 '17 at 18:41

30

List<Person> personsWithoutDuplicates = persons.stream()
 .distinct()
 .collect(Collectors.toList());

answered Nov 01 '17 at 18:41

Taras Melnyk

2,729
3
34
32

3

You sure that's going to work if the class does override equals and hash? – Robert Moskal Nov 01 '17 at 19:02
5

@RobertMoskal: the question is, rather, why you'd want to sneak around implementing `equals` and `hashCode` in the first place. – Priidu Neemre Oct 12 '18 at 10:03
distinct - Returns a stream consisting of the distinct elements (according to Object.equals(Object)) of this stream. – Taras Melnyk Apr 15 '22 at 09:15

score 1 · Answer 3 · edited Jan 27 '20 at 09:38

1

List<Person> modified = pesrons.stream().collect(Collectors.toCollection(()->new TreeSet<>(Comparator.comparing(Person::getName)))).stream().collect(Collectors.toList());

This will return a list of non duplicates based on Name.

You can refer this also Remove duplicates from a list of objects based on property in Java 8

edited Jan 27 '20 at 09:38

Timbus Calin

11,679
3
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51

answered Jul 31 '17 at 18:07

Rohit

331
1
5
15

score -3 · Answer 4 · answered Jan 27 '20 at 09:37

-3

public static void main(String[] args) {

    List<Integer> arrList = Arrays.asList(10, 20, 10, 30, 20, 40, 50, 40);

    arrList.stream().distinct().collect(Collectors.toList()).forEach(System.out::println);

}

answered Jan 27 '20 at 09:37

Manash Ranjan Dakua

185
1
7

How is this answer different from the one posted by Taras Melnyk years ago? Also note, that op uses Person instances, not integers. – BDL Jan 27 '20 at 11:39
My Answer is not belonging to others i am doing the distinct value operations using Integer class as Type Cast – Manash Ranjan Dakua Feb 20 '20 at 10:42

Remove duplicate from List java8

Person:

Testing:

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