[Rcpp-devel] Problem passing Armadillo objects back to R

Good news. I can reproduce it.
Bas news. This is likely a PROTECT problem with the Rcpp::List constructor.

Wearing my bugbuster costume, and getting ready for a fight.

Romain

Le 07/03/11 23:03, "G?nter J. Hitsch" a ?crit :

I'm new to Rcpp and RcppArmadillo---so far I like it a lot! Thanks to
the developers for their good work.

I run into a peculiar kind of problem when I try to pass a "large"
Armadillo object back to R. Here's some code to replicate the problem in
stylized form:


extern "C" SEXP testFun(SEXP L_)
{
const long L = Rcpp::as<long>(L_);
arma::mat X(L,1);
arma::mat Y(L,1);
X.fill(1);
Y.fill(2);
return Rcpp::List::create(
Rcpp::Named("X") = Rcpp::wrap(X),
Rcpp::Named("Y") = Rcpp::wrap(Y)
);
}


I compile (both using g++ and the Intel Compiler --- choice of compiler
makes no difference) and then call from R:


L = 1000000
ret = .Call("testFun", as.integer(L))
print(ret$X[1:5,])
print(ret$Y[1:5,])


Here's what I often get as output:

[1] 1 1 1 1 1
[1] 1 1 1 1 1

However, the second rows should be all 2's!

When I try to pass smaller matrices, for example by setting L=100000,
the problem goes away:

[1] 1 1 1 1 1
[1] 2 2 2 2 2


Also, the problem does not arise when I create and pass pack objects of
type Rcpp::NumericMatrix; so far I've see the problem only with
Armadillo objects. I've encountered this on two Macs running OS X
10.6.6, R 2.12.2, and I'm using the latest versions of Rcpp and
RcppArmadillo.

Help on this matter is appreciated!

G?nter