The inrange function is super useful, yet some applications only need a subset of at most k indices inside the range. This is particularly useful in hot loops because then it is possible to pre-allocate a buffer of length k once, and populate this buffer with a set of random indices inside the range.

How hard would it be to add a new knninrange function that achieves this goal? From what I understand, the following core function is responsible for adding indices to the final result of inrange:

Could we adjust the code to consider custom criteria besides check_in_range ̇?