I have the elements for a matrix as follows:
diag= rep(1,5)
offdiag = c(rep(1:4), rep(1:3), rep(1:2), 1)
The final matrix I want should should be a symmetric matrix that looks like this:
1 1 2 3 4
1 1 1 2 3
2 1 1 1 2
3 2 1 1 1
4 3 2 1 1
where the diagonal is filled by diag and the lower-trianglar area is filled by offdiag column-wise.
In practice, all all numbers are random. So I need a generic way to fill in the matrix with elements.
Thanks in advance!
Try this:
m <- matrix(NA, ncol = length(diag), nrow = length(diag))
m[lower.tri(m)] <- offdiag
m[upper.tri(m)] <- t(m)[upper.tri(t(m))]
diag(m) <- diag
m
# [,1] [,2] [,3] [,4] [,5]
# [1,] 1 1 2 3 4
# [2,] 1 1 1 2 3
# [3,] 2 1 1 1 2
# [4,] 3 2 1 1 1
# [5,] 4 3 2 1 1
Another alternative: Manually create a distance matrix and work from there.
class(offdiag) <- "dist"
attr(offdiag, "Size") <- length(diag)
out <- as.matrix(offdiag)
diag(out) <- diag
out
