def argsort(self, *args, **kwargs):
        if self._step > 0:
            return np.arange(len(self))
        else:
            return np.arange(len(self) - 1, -1, -1)
return an ndarray indexer of the underlying data
dataset/ETHPy150Open pydata/pandas/pandas/indexes/range.py/RangeIndex.argsort