search for: nonzero_m

I have a very sparse square matrix which is < 20K rows & columns and I am trying to row standardize the matrix for the rows that have non-missing value as follows: row_sums <- rowSums(M,na.rm=TRUE) nonzero_idxs <- which(row_sums>0) nonzero_M <- M[nonzero_idxs,]/row_sums[nonzero_idxs] M[nonzero_idxs,] <- nonzero_M Each line completes well under a second except the last line which takes well over 10 seconds which is simply assigning the sub-matrix of rows that have non-missing values to the complete matrix. I am curious to know wh...