title: Read a dense matrix from a file directly into a sparse numpy array?
body: <p>I have a matrix stored in a tab-separated format in a text file. It is stored densely, but I know it is very sparse. I want to load this matrix into one of Python's sparse formats. The matrix is very large, so doing a <code>scipy.loadtxt(...)</code> and then converting the resulting dense array to a sparse format would take too much RAM memory in the intermediate step, so that is not an option.</p>