Vedanth Vedanth - 1 year ago 75
Java Question

Java stream filter items of specific index

I'm looking for a concise way to filter out items in a List at a particular index. My example input looks like this:

List<Double> originalList = Arrays.asList(0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0);
List<Integer> filterIndexes = Arrays.asList(2, 4, 6, 8);

I want to filter out items at index
. I have a for loop that skips items that match the index but I was hoping there would be an easy way of doing it using streams. The final result would look like that:

List<Double> filteredList = Arrays.asList(0.0, 1.0, 3.0, 5.0, 7.0, 9.0, 10.0);

Answer Source

You can generate an IntStream to mimic the indices of the original list, then remove the ones that are in the filteredIndexes list and then map those indices to their corresponding element in the list (a better way would be to have a HashSet<Integer> for indices since they are unique by definition so that contains is a constant time operation).

List<Double> filteredList = 
    IntStream.range(0, originalList.size())
             .filter(i -> !filterIndexes.contains(i))