Import list to Rcpp - r

Question

I have a list (with list inside) in R and need import to C using Rcpp.
# R
MainList <- list()
MainList$myint <- 2
MainList$mylist <- list(matrix(1,2,2), matrix(2,2,2))
MainList
My goal is import the list in R (MainList$mylist in example) and copy to one 3D array in C.
I tried this:
// Rcpp
// [[Rcpp::export]]
List MyFunction (List MainList){
int N = as<int>(MainList["myint"]);
List mylistRcpp = as<List>(MainList["mylist"]); // It this work? Apparently no
double*** mylistC; // already with allocate memory
for (int h=0; h<N; h++){
NumericMatrix temp = mylistRcpp[h];
for (int i=0; i<N; i++){
for (int n=0; n<N; n++){
mylistC[h][i][n] = temp(i, n);
}
}
}
return List::create(Named("1") = N,
Named("2") = N);
}
I can import the list this way? There are some easy way to copy without copy one by one? I need the 3D array for another function. I not sure about how import the list from R to Rcpp.

Answer 1

Yes you can insert an Rcpp::List inside an Rcpp::List and recurse as deep as you want. No need for double** and other gymnastics.
Code
#include <Rcpp.h>
// [[Rcpp::export]]
Rcpp::List ListExample() {
std::string abc = "def";
double tol = 0.001;
Rcpp::List l = Rcpp::List::create(Rcpp::Named("method", abc),
Rcpp::Named("tolerance", tol));
Rcpp::List ll = Rcpp::List::create(Rcpp::Named("method", abc),
Rcpp::Named("tolerance", tol),
Rcpp::Named("list", l));
return ll;
}
/*** R
ListExample()
*/
Demo
R> sourceCpp("/tmp/soQ.cpp")
R> ListExample()
$method
[1] "def"
$tolerance
[1] 0.001
$list
$list$method
[1] "def"
$list$tolerance
[1] 0.001
R>
As you can see we have a list inside a list.