Create a new iterator from an existing iterator. The new iterator
will only return those elements that match the given compare function func.
func should return 0 for elements that should be included
in the iterator.
When this iterator is freed, it will also be freed.
Create a new iterator from an existing iterator. The new iterator will only return those elements that match the given compare function func. func should return 0 for elements that should be included in the iterator. When this iterator is freed, it will also be freed.