Concatenate two list by applying an operation in pairs using java stream

Question

I have two lists of Boolean and I need to concatenate them by applying an AND operation to the elements with the same index, I'm expecting to get a list of Booleans that contains the result of doing the operation in pairs.

public List<Boolean> concatenate(List<Boolean> l1, List<Boolean> l2) {

    return l1.stream()
                .flatMap(e1 -> l2.stream()
                                .filter(e2-> l1.indexOf(e1) == l2.indexOf(e2))
                                .map(e2-> e1&&e2))
                .collect(Collectors.toList());
}

The size of the resulting list will be l1.size()*l2.size() so the filter inside the second stream is filtering anything.

Answer 1

List<Boolean> l1 = new ArrayList<>(Arrays.asList(true, false, true));
List<Boolean> l2 = new ArrayList<>(Arrays.asList(false, true, true));

List<Boolean> l3 = IntStream.range(0, min(l1.size(), l2.size()))
                            .mapToObj(i -> l1.get(i)&&l2.get(i))
                            .collect(Collectors.toList());

// [false, false, true]

You can use IntStream.range() to iterate over both the lists at once and .mapToObj() to convert the && to Boolean and .collect() to store it in a new List.

You can simplify the range to .range(0, l1.size()) if you know for sure that both of them are of the same size.