Dump a sparse matrix into a file

Question

I have a scipy.sparse.csr matrix and would like to dump it to a CSV file. Is there a way to preserve the sparsity of the matrix and write it to a CSV?

Answer 1

SciPy includes functions that read/write sparse matrices in the MatrixMarket format via the scipy.io module, including mmwrite: http://docs.scipy.org/doc/scipy/reference/generated/scipy.io.mmwrite.html

MatrixMarket is not CSV, but close. It consists of a one-line header that has #rows, #cols, # of nonzeros, followed by one line per nonzero. Each of these lines is the row index, column index, value. You could write a simple script that turns whitespace into commas and you'd have a CSV.