[R] Efficent way to create an nxn upper triangular matrix of one's

[David Winsemius]

The other solutions offered are perfectly workable. Here is a strategy  
that is generalizable to other matrix designs (and on checking the  
source of upper.tri and lower.tri, it's not surprising that they use  
precisely the same strategy):

n <- 9
dm <- matrix(0, nrow=n, ncol=n)

dm[col(dm) >= row(dm)] <- 1

If you wanted only upper off-diagonal -1's, for instance, you could  
use instead:

dm[col(dm) == (row(dm)+1) ] <- -1

-- 
David Winsemius

On Feb 11, 2009, at 4:22 PM, Dale Steele wrote:

> The code below create an nxn upper triangular matrix of one's.  I'm
> stuck on finding a more efficient vectorized way - Thanks.  --Dale
>
> n <- 9
> data <- matrix(data=NA, nrow=n, ncol=n)
> data
> for (i in 1:n) {
>    data[,i] <- c(rep(1,i), rep(0,n-i))
> }
> data
>
> ______________________________________________
> 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.