Question

For example: I have a list of matrices, and I would like to evaluate their differences, sort of a 3-D diff. So if I have:

m1 <- matrix(1:4, ncol=2)
m2 <- matrix(5:8, ncol=2)
m3 <- matrix(9:12, ncol=2)
mat.list <- list(m1,m2,m3)

I want to obtain

mat.diff <- list(m2-m1, m3-m2)

The solution I found is the following:

mat.diff <- mapply(function (A,B) B-A, mat.list[-length(mat.list)], mat.list[-1])

Is there a nicer/built-in way to do this?

Answer 1

You can do this with just lapply or other ways of looping:

mat.diff <- lapply( tail( seq_along(mat.list), -1 ), 
                    function(i) mat.list[[i]] - mat.list[[ i-1 ]] )