[SciPy-user] Sparse csr_matrix and column sum

[Dinesh B Vadhia]

If A is a sparse csr_matrix and you want to calculate the sum of each column then the 'normal' method is:

import numpy
import scipy
from scipy import sparse

colSum = scipy.asmatrix(scipy.zeros((1,J), dtype=numpy.float))
colSum = A.mean(0)

This isn't working.  Do we have to do something else (eg. a todense()) for a sparse matrix?  If so, how?

Dinesh
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