[Rcpp-devel] How to modifying the elements of a list in the global environment?

[Giovanni Petris]

Hi Dirk,

Thank you for the quick reply. I will look for more examples on the net. 

About your suggestion of allocating scrap space inside the C++ routine, am I wrong to think that when the matrices are large and the function is called repeatedly within a Gibbs sampler loop, this is not a very efficient approach?

Thanks again!

Best,
Giovanni 

________________________________________
From: Dirk Eddelbuettel [edd at debian.org]
Sent: Thursday, October 18, 2012 8:06 PM
To: Dirk Eddelbuettel
Cc: Giovanni Petris; rcpp-devel at lists.r-forge.r-project.org
Subject: Re: [Rcpp-devel] How to modifying the elements of a list in the        global  environment?

Giovanni,

On 18 October 2012 at 17:46, Dirk Eddelbuettel wrote:
| | > code_f <- '
| | +     Rcpp::NumericMatrix cpp_x(x);
| | +     Rcpp::NumericMatrix cpp_mu(mu);
| | +     int K = cpp_mu.ncol();
| | +     int M = cpp_mu.nrow();
| | +     int N = cpp_x.nrow();
| | +     Environment glob = Environment::global_env();
| | +     List cpp_work(glob.get("workspace"));
| | +
| | +     for (int k=0; k < K; k++) {
| | +         cpp_work[k] = clone(cpp_x);
| | +         for (int i=0; i < M; i++)
| | +             cpp_work(_, i) = cpp_work(_, i) - cpp_mu(i, k);

That can't work.  You have the types confused.

You could just pass the list object down, and then pick from it.  Working
examples for that are in the list archives, in the RcppExamples package, and
in other places on the net.

Or, as I suggested, just allocate the scrap space inside the C++ routine.

Hth,  Dirk

--
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com