Intersection of two List<int[]> types by java streams

Question

List<int[]> bigList = new ArrayList<int[]>();
List<int[]> smallList = new ArrayList<int[]>();

I need to generate a List of type int[] with the common arrays form both the lists.(values should be equal , not using the contains())

How to do it efficiently in java streams??

Answer 1

If it really has to be a stream solution, here’s one:

List<int[]> intersection=bigList.stream().map(IntBuffer::wrap)
    .filter(b->smallList.stream().map(IntBuffer::wrap).anyMatch(b::equals))
    .map(IntBuffer::array)
    .collect(Collectors.toList());

but it isn’t really efficient by performing up to bigList.size()×smallList.size() operations. So instead of doing everything on-the-fly, resorting to an intermediate Set storage is strongly recommended:

Set<IntBuffer> bigSet=bigList.stream().map(IntBuffer::wrap).collect(Collectors.toSet());
List<int[]> intersection=smallList.stream().map(IntBuffer::wrap)
     .filter(bigSet::contains).map(IntBuffer::array).collect(Collectors.toList());

Note that you shouldn’t use List for set operations. The semantics of source and result ordering and how to handle duplicates within the source lists are unspecified.