How can I add two IntStreams element by element?

Question

Example;

IntStream a = create(3, 1);  // => [0,0,1]
IntStream b = create(5, 2);  // => [0,0,0,0,2]

The first stream gives an infinite stream of [0,0,1,0,0,1...] and the second an infinite stream of [0,0,0,0,2,0,0,0,0,2,...].

The result stream is ri = ai + bi meaning that I just want to take the sum of the elements at the same position from each stream.

Is this possible in Java ?

Implementing a `Spliterator` is apparently the best method: https://stackoverflow.com/q/30685623/1896169 — Justin, May 22 '17 at 19:37
Also very relevant: https://stackoverflow.com/q/17640754/2988730 — Mad Physicist, May 22 '17 at 19:43
i'm really don't get it, i'm not familiar so much with streams so i don't know how create look like @MadPhysicist can you guide me please? — YCF_L, May 22 '17 at 19:43
@YCF_L For test purposes, just have an ArrayList with 15 elements for each case and call `toStream` or whatever on it. No need to make this complicated — Mad Physicist, May 22 '17 at 19:45
So, the result for the given example with `[0, 0, 1, …]` and `[0, 0, 0, 0, 2, …]` would be `[0, 0, 1, 0, 2, 1, …]`? — beatngu13, May 22 '17 at 19:56
@beatngu13. If the 15th element is 3, then yes. This looks like FizzBuzz now that you put it that way. — Mad Physicist, May 22 '17 at 19:58
Possible duplicate of [Zipping streams using JDK8 with lambda (java.util.stream.Streams.zip)](https://stackoverflow.com/questions/17640754/zipping-streams-using-jdk8-with-lambda-java-util-stream-streams-zip) — Ole V.V., May 22 '17 at 20:08

score 2 · Answer 1 · answered May 22 '17 at 20:18

2

You can use Guava's Streams.zip() helper:

IntStream sum(IntStream a, IntStream b) {
    return Streams.zip(a.boxed(), b.boxed(), Integer::sum)
            .map(Integer::intValue);
}

answered May 22 '17 at 20:18

shmosel

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Dmitry P. · Answer 2 · 2017-05-23T16:53:11.130

You can define your own Spliterator to create a stream from it later.

import java.util.Comparator;
import java.util.Spliterators;
import java.util.function.IntConsumer;

public class SumSpliterator extends Spliterators.AbstractIntSpliterator {
    private OfInt aSplit;
    private OfInt bSplit;

    SumSpliterator(OfInt a, OfInt b) {
        super(Math.min(a.estimateSize(), b.estimateSize()), Spliterator.ORDERED);
        aSplit = a;
        bSplit = b;
    }

    @Override
    public boolean tryAdvance(IntConsumer action) {
        SummingConsumer consumer = new SummingConsumer();
        if (aSplit.tryAdvance(consumer) && bSplit.tryAdvance(consumer)) {
            action.accept(consumer.result);
            return true;
        }
        return false;
    }

    static class SummingConsumer implements IntConsumer {
        int result;
        @Override
        public void accept(int value) {
            result += value;
        }
    }
}

Then create a stream and check the results

IntStream a = //create stream a
IntStream b = //create stream b
SumSpliterator spliterator = new SumSpliterator(a.spliterator(), b.spliterator());
Stream<Integer> stream = StreamSupport.stream(spliterator, false);
stream.limit(20).forEach(System.out::println);

I’d use `Math.min(a.estimateSize(), b.estimateSize())` as estimated size… — Holger, May 23 '17 at 11:14

How can I add two IntStreams element by element?

2 Answers2