ENH: Reverse parameter in np.sort()

Currently, in order to sort an array in reverse order you have to use some form of strange hack, which may or may not be guaranteed to work in the future.

I suggest adding a reverse parameter to np.sort, similar to the native Python sort() function. This would make the hacks unnecessary and improve readability of code, by making the sorting order explicit.

This feature should not result in any performance problems - after all, the sorting function simply have to reverse the boolean result when comparing values.

Reproducing code example:

import numpy as np

a = np.arange(10)
np.random.shuffle(a)
a.sort(reverse = True)
print(a) # should print "[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]"

[eric-wieser]

I just wanted to chime in here that you can already get reversed sorting without any copies with ndarray.sort and indexing:

This approach does not result in a stable sort

[seberg]

Interestingly, the here “descending” is used. I am a bit uncertain about that choice, since it is at odds with Pythons sorted and sort.

In general, we should probably solve this in C, this may require adding more sorting “methods” in C, which was not possible for a long time.

However, NEP 41+43 now makes it possible in a pretty straight-forward manner. I could help with that first step (extending the machinery, or at least providing a blueprint for it), but I don’t think I can commit time to the feature itself. If anyone can make it a their larger project, please let me know so I can help with that first step. (It is pretty new API, so there is no direct blueprint, me making a start on it would probably safe a lot of time for anyone diving into it.)