copy a subset of the entries index to the other index
if subset_type == 0: copies ids in [a1, a2)
if subset_type == 1: copies ids if id % a1 == a2
if subset_type == 2: copies inverted lists such that a1
elements are left before and a2 elements are after
copy a subset of the entries index to the other index
if subset_type == 0: copies ids in [a1, a2) if subset_type == 1: copies ids if id % a1 == a2 if subset_type == 2: copies inverted lists such that a1 elements are left before and a2 elements are after