How to zip multiple lists using java 8?

Question

Given :

List<Integer> a = Arrays.asList(1,2,3);
List<Integer> b = Arrays.asList(1,2,3);
List<Integer> c = Arrays.asList(1,2,3);
List<Integer> d = Arrays.asList(1,2,3);

List<List<Integer>> sample = Arrays.asList(a,b,c,d);

How can I get this result with java 8?

[(1,1,1,1),(2,2,2,2),(3,3,3,3)]

Answer 1

/**
 * Zips lists. E.g. given [[1,2,3],[4,5,6]], returns [[1,4],[2,5],[3,6]].
 * @param listOfLists an N x M list
 * @returns an M x N list
 */
static <T> List<List<T>> zip(List<List<T>> listOfLists) {
    int size = listOfLists.get(0).size();
    List<List<T>> result = new ArrayList<>(size);
    for (int i = 0; i < size; ++i)
        result.add(
                listOfLists.stream()
                        .map(list -> list.get(i))
                        .collect(toList()));
    return result;
}

Answer 2

Java streams don't natively support zipping.

If you want to do it manually, then using an IntStream as an 'iterator' over the lists is the way to go:

    List<Integer> l1 = Arrays.asList(1, 2, 3);
    List<Integer> l2 = Arrays.asList(2, 3, 4);

    List<Object[]> zipped = IntStream.range(0, 3).mapToObj(i -> new Object[]{l1.get(i), l2.get(i)}).collect(Collectors.toList());

    zipped.stream().forEach(i -> System.out.println(i[0] + " " + i[1]));

This is ugly, however, and not the 'java' way (as in using an array of 'properties' instead of a class).