R help - Feb 2009 - Efficent way to create an nxn upper triangular matrix of one's

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

Try

x <- diag(n)
x[upper.tri(x)] <- 1

On Wed, Feb 11, 2009 at 1:22 PM, Dale Steele <dale.w.steele at gmail.com>
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.
>

Dear Dale,
Here is one way, probably not the best:

n<-9
temp<-matrix(1,ncol=n,nrow=n)
temp[lower.tri(temp)] <- 0
temp

HTH,

Jorge


On Wed, Feb 11, 2009 at 4:22 PM, Dale Steele
<dale.w.steele@gmail.com>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@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.
>
	[[alternative HTML version deleted]]

Here is a way to do this:

round(upper.tri(matrix(1, 9, 9)))

Or if you also need the diagonal of one's

round(upper.tri(matrix(1, 9, 9), diag = TRUE))

-Christos 
 
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Dale Steele
> Sent: Wednesday, February 11, 2009 4:23 PM
> To: R help
> Subject: [R] Efficent way to create an nxn upper triangular 
> matrix of one's
> 
> 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.
> 
>

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.