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

[Dirk Eddelbuettel]

On 19 October 2012 at 01:32, Giovanni Petris wrote:
| 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?

Yes, if you want to use it several times you can pass it around for reuse.
As I mentioned, a reference is just a pointer and hence unrelated to the size
of the object.

Dirk
 
| 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

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