Dear R-users,
would it be a better way to construct the matrix below without using any
for-loop or model.matrix? preferably with some matrix algebra?
Thanks in advance,
Carlo Giovanni Camarda
## dimensions
m <- 3
n <- 4
mn <- m*n
k <- m+n-1
## with a for-loop
X <- matrix(0, mn, k)
for(i in 1:n){
wr <- 1:m+(i-1)*m
wc <- rev(1:m+(i-1))
where <- cbind(wr,wc)
X[where] <- 1
}
## using model.matrix
ff <- factor(c(outer(m:1, seq(0,m), "+")))
X1 <- matrix(model.matrix(~-1+ff), mn, k)
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