Does this do what you want? > d <- col(mat) - row(mat) > tapply( mat, d, sum )
Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare [EMAIL PROTECTED] (801) 408-8111 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Camarda, > Carlo Giovanni > Sent: Tuesday, February 26, 2008 1:32 PM > To: [EMAIL PROTECTED] > Subject: [R] Summing up diagonals w/o for-loop > > Dear R-users, > > is there any way to sum up the elements of the "diagonals" of > a matrix without using a for-loop? While there is a simple > way over rows and columns, I don't see a straightforward > multiplication for the diagonals, am I too demanding? Or, > more likely, I'm lack some algebra trick? Is there any > R-function that can deal with this problem w/o loop? > > Actually I would need to sum up just the upper diagonals. > > Here a simple, but general, example for presenting the problem. > > Thanks in advance for any help, > Carlo Giovanni Camarda > > m <- 7 > n <- 5 > mat <- matrix(1:35, n, m) > ones.r <- rep(1,n) > ones.c <- rep(1,m) > # sum over the rows > sum.r <- mat%*%ones.c > # sum over the cols > sum.c <- t(mat)%*%ones.r > # sum over the diags > sum.d <- numeric(m+n-1) > sum.d[1] <- mat[n,1] > sum.d[m+n-1] <- mat[1,m] > for(i in 2:n){ > sum.d[i] <- sum(diag(mat[(n+1-i):n,1:i])) } for(i in 2:(m-1)){ > sum.d[i+n-1] <- sum(diag(mat[,i:m])) } > > > > ---------- > This mail has been sent through the MPI for Demographic > ...{{dropped:10}} > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
