Remove from ArrayList if one value of objects repeats

Question

How to remove duplicate object from ArrayList, but only if one specific value from object repeats with another object?

For example: I have class named Person with fields:

private String city;
private String firstName;
private String lastName;
private Long magicNumber;

I want to remove "older" Person with same "magicNumber" as the new One and keep him in ArrayList.

overwrite - remove lower index from ArrayList with same "magicNumber" — tomasz pawlak, Mar 04 '20 at 19:09
https://stackoverflow.com/questions/29670116/remove-duplicates-from-a-list-of-objects-based-on-property-in-java-8 — Guillermo Nahuel Varelli, Mar 04 '20 at 19:17
I would rather override hashCode and equals + use Set https://stackoverflow.com/questions/53371148/treeset-comparator-failed-to-remove-duplicates-in-some-cases — Evgeniy, Mar 04 '20 at 19:44

score 3 · Accepted Answer · answered Mar 04 '20 at 19:34

3

Using streams :

Collection<Person> filterd = persons.stream()
            .collect(Collectors.toMap(
                    Person::getMagicNumber, p -> p, (p1, p2) -> p2))
            .values();

answered Mar 04 '20 at 19:34

Eritrean

15,851
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1

@tomaszpawlak Glad i could help. – Eritrean Mar 04 '20 at 19:57

Huatxu · Answer 2 · 2020-03-04T19:38:49.260

0

Well, assuming you have overriden public boolean equals(Object object) in your class in order to compare your magicNumber field:

https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#equals(java.lang.Object)

List<Person> persons = new ArrayList<>();
public void addToList(Person person) {
     if(persons.contains(person)) {
         persons.set(persons.indexOf(person), person);
     } else {
         persons.add(person);
     }

}

edited Mar 04 '20 at 19:38

answered Mar 04 '20 at 19:09

Huatxu

111
5

there is no `replace` method in `List`, you probably meant `set(int, Object)`. Also, you could remove the `contains`, calculate the index beforehand and then check if it is `< 0` in the condition. – Clashsoft Mar 04 '20 at 19:38

score -1 · Answer 3 · answered Mar 04 '20 at 19:53

-1

public void addPerson(Person p) {
    list.removeIf(o -> o.magicNumber.equals(p.magicNumber));
    list.add(p);
}

answered Mar 04 '20 at 19:53

Ryan

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Remove from ArrayList if one value of objects repeats

3 Answers3