Return the integer indices that would sort the Series values.
Override ndarray.argsort. Argsorts the value, omitting NA/null values,
and places the result in the same locations as the non-NA values.
Has no effect but is accepted for compatibility with numpy.
Choice of sorting algorithm. See numpy.sort() for more
information. ‘mergesort’ and ‘stable’ are the only stable algorithms.
Positions of values within the sort order with -1 indicating
Returns the indices that would sort this array.