Calculate the matrix matrix of rows by vector

Question

For a vector, I would like to create a square matrix in which the elements of the vector are located diagonally, and there is a line with the outline of the elements.

Vector example:

vec <- c(1, 2, 3, 4) 

Required Conclusion:

  [,1] [,2] [,3] [,4] [1,] 1 3 6 10 [2,] 0 2 5 9 [3,] 0 0 3 7 [4,] 0 0 0 4 

Now I use the double function for the loop:

 diagSum <- function(vec) { mat <- diag(vec) for (i in seq(nrow(mat))) { for (j in seq(i, ncol(mat))) { if (j > i) { mat[i, j] <- mat[i, j - 1] + mat[j, j] } } } mat } 

What will the R-way (avoiding for loops) do this?

Answer 1

 m <- matrix(vec, nrow = length(vec), ncol = length(vec), byrow =TRUE) m[lower.tri(m)] <- 0 t(apply(m, 1, cumsum)) # [,1] [,2] [,3] [,4] #[1,] 1 3 6 10 #[2,] 0 2 5 9 #[3,] 0 0 3 7 #[4,] 0 0 0 4 

Answer 2

One way to do this:

 x <- c(1, 2, 3, 4) rbind(cumsum(x), t(sapply(1:3, function(y) c(rep(0, y), cumsum(x[-(1:y)])) ))) # [,1] [,2] [,3] [,4] # [1,] 1 3 6 10 # [2,] 0 2 5 9 # [3,] 0 0 3 7 # [4,] 0 0 0 4 

Answer 3

Like this:

 > x=c(1, 2, 3, 4) > do.call(rbind, lapply(1:length(x)-1, function(u) {x[0:u]=0;cumsum(x)})) # [,1] [,2] [,3] [,4] #[1,] 1 3 6 10 #[2,] 0 2 5 9 #[3,] 0 0 3 7 #[4,] 0 0 0 4