Remove multiple elements from ArrayList

Question

I have a bunch of indexes and I want to remove elements at these indexes from an ArrayList. I can't do a simple sequence of remove()s because the elements are shifted after each removal. How do I solve this?

Answer 1

To remove elements at indexes:

Collections.sort(indexes, Collections.reverseOrder()); for (int i : indexes)     strs.remove(i); 

Or, using the Stream API from Java 8:

indexes.sort(Comparator.reverseOrder()); indexes.stream().mapToInt(i -> i).forEach(l::remove); 

Answer 2

Sort the indices in descending order and then remove them one by one. If you do that, there's no way a remove will affect any indices that you later want to remove.

How you sort them will depend on the collection you are using to store the indices. If it's a list, you can do this:

List<Integer> indices; Collections.sort(indices, new Comparator<Integer>() {    public int compare(Integer a, Integer b) {       //todo: handle null       return b.compareTo(a);    } } 

Edit

@aioobe found the helper that I failed to find. Instead of the above, you can use

Collections.sort(indices, Collections.reverseOrder());