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javajava-stream
Vladimir Krekic
Vladimir Krekic

Reputation: 55

How can I filter elements of the list based on their index(position) using stream() in Java?

How can I filter elements of the list based on their index(position) using stream() in Java? I want to filter every third element (i.e. indices 0, 3, 6, 9,... of a List<String>).

Upvotes: 0

Views: 1522

Answers (2)

Samuel Philipp
Samuel Philipp

Reputation: 11050

Since Java 9 you can use IntStream.iterate() to achieve that:

IntStream.iterate(0, i -> i < list.size(), i -> i + 3)
        .mapToObj(list::get)
        .forEach(System.out::println);

If you are using Java 8 you can use this:

IntStream.iterate(0, i -> i + 3)
        .limit(list.size() / 3)
        .mapToObj(list::get)
        .forEach(System.out::println);

Edit: As Holger pointed out in the comments a more efficient solution would be this:

IntStream.range(0, list.size() / 3)
        .mapToObj(i -> list.get(i * 3))
        .forEach(System.out::println);

Upvotes: 3

Eran
Eran

Reputation: 394156

You'll have to use an IntStream.

For example, the following will create a Stream containing all the List elements whose indices are divisible by 3:

List<String> yourList = ...
IntStream.range(0,yourList.size()) // IntStream of 0,1,2,3,...
         .filter(i -> i % 3 == 0) // IntStream of 0,3,6,...
         .mapToObj(yourList::get) // Stream<String> of yourList.get(0),yourList.get(3),...
         ...

Upvotes: 2

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