Adding a column of zeroes to a csr_matrix

Question

I have an MxN sparse csr_matrix, and I\'d like to add a few columns with only zeroes to the right of the matrix. In principle, the arrays indptr, <

Answer 1

You can use scipy.sparse.vstack or scipy.sparse.hstack to do it faster:

from scipy.sparse import csr_matrix, vstack, hstack

B = csr_matrix((5, 2), dtype=int)
C = csr_matrix((5, 2), dtype=int)
D = csr_matrix((10, 10), dtype=int)

B2 = vstack((B, C))
#<10x2 sparse matrix of type ''
#        with 0 stored elements in COOrdinate format>

hstack((B2, D))
#<10x12 sparse matrix of type ''
#        with 0 stored elements in COOrdinate format>

Note that the output is a coo_matrix, which can be efficiently converted to the CSR or CSC formats.