Python: find count of non-zero elements in a compressed sparse matrix

Question

How can I find the total number of non-zero elements in a CSR matrix?

Answer 1

count_nonzero() function of csr_matrix returns the actual number of non-zero entries in the sparse matrix. So, you can use it to find the count.

Here is an example:

>>> import numpy as np
>>> from scipy.sparse import csr_matrix
>>> row = np.array([0, 0, 1, 2, 2, 2])
>>> col = np.array([0, 2, 2, 0, 1, 2])
>>> data = np.array([1, 1, 1, 1, 1, 1])
>>> X=csr_matrix((data, (row, col)), shape=(3, 3))
>>> X.toarray()
array([[1, 0, 1],
       [0, 0, 1],
       [1, 1, 1]])
>>> X.count_nonzero()
6