update: came across Simon's
http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2013-June/006080.htmlpost,
where Romain suggested c++11 move constructor; which is supported
in the latest Armadillo release;
for the record here are the tested working solutions, if found to be useful
for others and there is a way to add these to RcppArmadillo examples, I can
send the code in required format.
thanks again for everyone's contribution,
steve
/*
---------------------------------------------------------- code c++11
-------------------------------------------------------------------------
*/
#include <R.h>
#include <stdlib.h>
#include <RcppArmadillo.h>
#include <utility>
using namespace std;
// [[Rcpp::depends(RcppArmadillo)]]
// suggested by Simon, pointer solution, this has a disadvantage of extra
de referencing
// which is ok inside class methods, but somewhat awkward when matrix is
public
// has the advantage that doesn't need c++11 and latest Armadillo
struct Example {
Example(double *ptr) {
A= new arma::mat(ptr, 3,2, false, true ); // same area as original B
arma::mat &a = *A; // dereference B
a(1,1) = 1; // convenient matlab like syntax
}
~Example(){ delete A; }
arma::mat *A;
};
// this is moving constructor works only with c++11 and latest Armadillo
// much nicer syntax; the 'view' is encapsulated, and invisible;
struct Example1 {
Example1(double *ptr ) : A(arma::mat(ptr, 3,2, false, true ) ){
A(1,1) = 3;
}
arma::mat A;
};
// this is moving constructor works only with c++11 and latest Armadillo
// much nicer syntax, referenced matrix constructed with move contructor
struct Example2 {
Example2(arma::mat m ) : A(m){ // 'view' is not visible from the inside
A(2,1) = 4;
}
arma::mat &A;
};
// [[Rcpp::depends(RcppArmadillo)]]
// [[Rcpp::export]]
void arma_example() {
arma::mat M(3,10); // implicit memory allocation; of course this can be
done many other ways
// Dirk suggestions using bigmemory and or
R matrix passed with Rcpp proxy
// depending on needs
M.zeros(); // paint with zeros
M.print(); cout<<endl<<endl;
// this is the main part: arma::mat submatrix has read write access to M
without copy!;
// inside of Example? classes one can operate on some part of M
Example E(M.memptr());
M.print();cout<<"-------------"<<endl;
Example1 E1( M.memptr() );
M.print(); cout<<"-------------"<<endl;
Example2 E2( arma::mat( M.memptr(), 3,2, false, true ) );
M.print();cout<<"-------------"<<endl;
}
// EOF
On Tue, Nov 26, 2013 at 7:38 PM, Steven Varga <steven.va...@gmail.com>wrote:
> Hello Simon,
>
> my apologies contacting you off the list; I try to avoid confusion.
>
> I came across your previous post:
> http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2013-June/006080.htmlwhere
> you seemed to have similar issues to mine: creating an arma::mat with
> external storage, then bumping into '=' operator which does deep copy;
>
> I just noticed that the newest version of Armadillo supports c++11 move
> constructor; did you have a chance to try it?
>
> Steve
>
>
> On Tue, Nov 26, 2013 at 6:19 AM, <szehn...@uni-bonn.de> wrote:
>
>> Steve,
>>
>> If you want to use a variable being an arma::mat obejct with varying
>> memory, you could use an arma::mat pointer. Otherwise if memory stays the
>> same but should be reusable in R, Dirk's suggestion initialising memory in
>> R and passing it to C++ is the most practicable way and very fast.
>>
>> Best
>> Simon
>> Gesendet über den BlackBerry® Service von E-Plus.
>>
>> -----Original Message-----
>> From: Steven Varga <steven.va...@gmail.com>
>> Sender: rcpp-devel-bounces@lists.r-forge.r-project.orgDate: Mon, 25 Nov
>> 2013 23:23:24
>> To: <rcpp-devel@lists.r-forge.r-project.org>
>> Reply-To: steven.va...@gmail.com
>> Subject: Re: [Rcpp-devel] RcppArmadillo matrix with writeable auxiliary
>> memory
>>
>> _______________________________________________
>> 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
>>
>
>
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