S4 object in R cannot be passed to Fortran

Question

I use the bdiag function in the Matrix package in R to generate diagonal matrix, and then I pass the resultant matrix (called mat) into a self-written function but R fails to execute due to the following error:

Error: invalid mode (S4) to pass to Fortran (arg 1)

I checked isS4(mat) and it's TRUE. Thus, I guess there is a way to convert the S4 object somehow in order to be passed to the function. Any advice will be greatly appreciated!

UPDATE: I use the following codes for constructing the block diagonal matrix:

grp.ids <- as.factor(c(rep(1,8), rep(2,4), rep(3,2)))
x <- model.matrix(~grp.ids)
X <- do.call(bdiag, replicate(238, x, simplify=FALSE))

Is there any other way to get a S3 matrix without using the bdiag function? Thanks!

Answer 1

Only the .Call() interface can pass full R objects down to C or C++ code, see Section 5 of the Writing R Extensions manual. With .Fortran() and .C() you are limited to basic vectors of int, double, ... and their corresponding Fortran types.