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

Something like this works for arbitrary dimensions-

ind2sub = function(sz,ind)
{
    ind = as.matrix(ind,ncol=1);
    sz = c(1,sz);
    den = 1;
    sub = c();
    for(i in 2:length(sz)){
        den = den * sz[i-1];
        num = den * sz[i];
        s = floor(((ind-1) %% num)/den) + 1;
        sub = cbind(sub,s);
    }
    return(sub);
}