Add unique_counts()?

[leofang]

This is a follow-up of #275. I've found numpy.unique(x, return_counts=True) quite useful. It allows us to build a histogram for the input array x. I'd suggest us to add the following function:

def unique_counts(x, /):
   """
   return a tuple of two arrays (unique values and counts)
   """

[leofang]

Can we target this for v2021?

[kgryte]

We'd be cutting this quite close. :)

Quite close that is for getting support from other array libraries that this is something we want to add for the 2021 revision.

[leofang]

I see. I know NumPy/CuPy have no problem in supporting this, but I am not sure about others.

[leofang]

I'll work on this as per the discussion in today's call.

[kgryte]

Thanks @leofang!

[rgommers]

Seems very reasonable, and if we add it we should indeed add it to the v2021 milestone. Better to do all four new unique_* functions in one go.