python - Is there an efficient way of concatenating scipy.sparse matrices?

Question

I'm working with some rather large sparse matrices (from 5000x5000 to 20000x20000) and need to find an efficient way to concatenate matrices in a flexible way in order to construct a stochastic matrix from separate parts.

Right now I'm using the following way to concatenate four matrices, but it's horribly inefficient. Is there any better way to do this that doesn't involve converting to a dense matrix?

rmat[0:m1.shape[0],0:m1.shape[1]] = m1
rmat[m1.shape[0]:rmat.shape[0],m1.shape[1]:rmat.shape[1]] = m2
rmat[0:m1.shape[0],m1.shape[1]:rmat.shape[1]] = bridge
rmat[m1.shape[0]:rmat.shape[0],0:m1.shape[1]] = bridge.transpose()

Answer 1

The sparse library now has hstack and vstack for respectively concatenating matrices horizontally and vertically.