def _min_or_max_axis(self, axis, min_or_max):
        N = self.shape[axis]
        if N == 0:
            raise ValueError("zero-size array to reduction operation")
        M = self.shape[axis - 1]

        mat = self.tocsc() if axis == 0 else self.tocsr()
        mat.sum_duplicates()

        major_index, value = mat._minor_reduce(min_or_max)
        not_full = np.diff(mat.indptr)[major_index] < N
        value[not_full] = min_or_max(value[not_full], 0)

        mask = value != 0
        major_index = np.compress(mask, major_index)
        value = np.compress(mask, value)

        from . import coo_matrix
        if axis == 0:
            return coo_matrix((value, (np.zeros(len(value)), major_index)),
                              dtype=self.dtype, shape=(1, M))
        else:
            return coo_matrix((value, (major_index, np.zeros(len(value)))),
                              dtype=self.dtype, shape=(M, 1))
dataset/ETHPy150Open scipy/scipy/scipy/sparse/data.py/_minmax_mixin._min_or_max_axis/swapped operands of `-`