The fastLm examples are nice but they don't contain anything relating to
passing an XPtr between functions. Regarding your comment about making an
XPtr around arma::mat 'innards' I'm not sure I fully understand. I tried
creating an XPtr around a arma::mat but no success on passing the object
between functions. It still returns that ~zeros.
// [[Rcpp::export]]
SEXP testXptr(SEXP A)
{
arma::Mat<double> armaMat = as<arma::mat>(A);
XPtr<arma::mat> pMat(&armaMat);
return(pMat);
}
// [[Rcpp::export]]
void testReturn(SEXP ptrA, int nr, int nc)
{
XPtr<arma::mat> ptrB(ptrA);
arma::mat B = arma::mat( (double *) ptrB->memptr(),
nr,
nc,
false);
B.print("copied matrix");
}
Charles
On Wed, Jun 24, 2015 at 8:32 AM, Dirk Eddelbuettel <e...@debian.org> wrote:
>
> On 24 June 2015 at 08:22, Charles Determan wrote:
> | Thank you John,
> |
> | I am familiar with bigmemory (I am one of the current developers
> actually).
> | The project I am working on doesn't need the shared memory aspect so was
> | intending to avoid the dependency and just leverage the more familiar and
> | developed Armadillo library. However your response informs me that I
> did not
> | fully understand how armadillo objects are handled. I have some other
> ideas
> | with how I can address my problem but this was something I was hoping to
> apply
> | both for this project and for the sake of learning.
>
> Look at more current RcppArmadillo examples, and in particular _all_ the
> variants of the fastLm benchmark in examples. By doing the explicit cast,
> you _forced_ a copy which may then have destroyed the Xptr link. I *think*
> you could just do XPtr around arma::mat innards. I would actually be
> interested in having something somewhere between bigmemory (where I was one
> of the first external users) and what we have in RcppArmadillo.
>
> Dirk, during a break of Rcpp class in Zuerich
>
> | Regards,
> | Charles
> |
> | On Tue, Jun 23, 2015 at 9:29 PM, John Buonagurio <
> jbuonagu...@exponent.com>
> | wrote:
> |
> | Hi Charles,
> |
> | > SEXP testXptr(SEXP A)
> | > {
> | > arma::Mat<double> armaMat = Rcpp::as<arma::Mat<double> >(A);
> | > Rcpp::XPtr<double> pMat(armaMat.memptr());
> | > return(pMat);
> | > }
> |
> | armaMat is on the stack, so the Armadillo memptr is no longer valid
> when
> | you return from the testXptr function.
> |
> | One simple solution in your case would be to dynamically allocate
> with
> | "new" [e.g. arma::mat *A = new arma::mat(...);], though I can't tell
> you
> | off hand how object lifetime is managed with Armadillo objects.
> |
> | If you're trying to preserve a matrix across function calls in R,
> have you
> | looked into bigmemory? http://gallery.rcpp.org/articles/
> | using-bigmemory-with-rcpp/
> |
> | John
> |
> |
> |
> | _______________________________________________
> | Rcpp-devel mailing list
> | Rcpp-devel@lists.r-forge.r-project.org
> | https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>
> --
> http://dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org
>
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