Converting between matrix subscripts and linear indices (like ind2sub/sub2ind in matlab)

Question

Let\'s say you have a matrix

m <- matrix(1:25*2, nrow = 5, ncol=5)

How do you go from matrix subscripts (row index, column index) to a lin

Answer 1

There are row and col functions that return those indices in matrix form. So it should be as simple as indexing the return from those two functions:

 M<- matrix(1:6, 2)
 row(M)[5]
#[1] 1
 col(M)[5]
#[1] 3
 rc.ind <- function(M, ind) c(row(M)[ind], col(M)[ind] )
 rc.ind(M,5)
[1] 1 3