From: Greg Snow <Greg.Snow_at_imail.org>

Date: Tue, 26 Feb 2008 13:48:10 -0700

Date: Tue, 26 Feb 2008 13:48:10 -0700

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 greg.snow_at_imail.org (801) 408-8111Received on Tue 26 Feb 2008 - 20:52:07 GMT

> -----Original Message-----

> From: r-help-bounces_at_r-project.org> [mailto:r-help-bounces_at_r-project.org] On Behalf Of Camarda,> Carlo Giovanni> Sent: Tuesday, February 26, 2008 1:32 PM> To: r-help_at_stat.math.ethz.ch> 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_at_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_at_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.

Archive maintained by Robert King, hosted by
the discipline of
statistics at the
University of Newcastle,
Australia.

Archive generated by hypermail 2.2.0, at Tue 26 Feb 2008 - 21:30:17 GMT.

*
Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help.
Please read the posting
guide before posting to the list.
*