Failure case for sparse max() function

example.py

In [28]: x = np.zeros((3, 3), float)

In [29]: x[0, 0] = -3.2

In [30]: x[2, 1] = -2.7

In [31]: s = sparse.csr_matrix(x)

In [32]: s.data
Out[32]: array([-3.2, -2.7])

In [33]: cpaste
Pasting code; enter '--' alone on the line to stop or use Ctrl-D.
:def sparse_max_row(csr_mat):
:    ret = np.zeros(csr_mat.shape[0])
:    ret[np.diff(csr_mat.indptr) != 0] = np.maximum.reduceat(csr_mat.data,csr_mat.indptr[:-1][np.diff(csr_mat.indptr)>0])
:    return ret
:
:--

In [34]: sparse_max_row(s)
Out[34]: array([-3.2,  0. , -2.7])