Calculate mean value per row of sparse matrix

sample.py

import numpy
from scipy.sparse import csr_matrix
A = numpy.array([[0, 0, 1],[0,2,4]])
# array([[0, 0, 1],
#        [0, 2, 4]])
B = csr_matrix(A)
d = B.getnnz(axis=1) # Get number of non zero entries
print(d)
# array([1, 2], dtype=int32)
print(B.sum(axis=1).A.reshape(-1)/d)
# array([1., 3.])