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
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