[Numpy-discussion] Re: ENH: Add "where" argument to reduction functions that are missing it

This also applies to - https://numpy.org/doc/stable/reference/generated/numpy.argmax.html - https://numpy.org/doc/stable/reference/generated/numpy.argmin.html and their nan* counterparts. An `initial` argument could be added to handle the empty case, as with np.max and np.min.