title: How to drop rows of an SpMat<unsigned int> in Armadillo based on a condition on row totals?
body: <p>Is there an efficient approach to only retain rows of an Armadillo sparse matrix that sum up to at least some level of total count across columns of the matrix? For instance, I would want to retain the <code>i</code>th row, if the sum of its values is <code>&gt;=C</code>, where <code>C</code> is some chosen value. Armadillo's documentation says that only contiguous submatrix views are allowed with sparse matrices. So I am guessing this is not easily obtainable by sub-setting. Is there an alternative to plainly looping through elements and creating a new sparse matrix with new locations, values and colPtr settings that match the desired condition? Thanks!</p>