[Rcpp-devel] how to create an Rcpp::List in a standalone C++ application?

[Florian Oswald]

Thanks Dirk and Romain,

Let me follow up on this if you don't mind, there's probably a lot of ways
to improve what I'm doing. Dirk, you mentioned blitz++. What I'm doing at
the moment is a bit contrived and I'm wondering whether there may be a
better way of going back and forth from R to blitz. my program looks like
this:

#include <blitz/array.h>

//' R interface to 3D Blitz++
//'
// [[Rcpp::export]]
NumericVector BlitzFun( NumericVector a_ , IntegerVector d){

    // map NumericVector to blitz++ array
    blitz::Array<double,3> a(a_.begin(), blitz::shape(d(0),d(1),d(2))
,blitz::neverDeleteData );

    // do some blitz
    blitz::Array<double,3> b(a + 1.2);

    //return wrap(b); does not work - obviously. would a wrap() method be
complicated?

    // instead copy back to a NumericVector
    NumericVector result(b.size());
    result = b;
    // and attach dimension attr
    result.attr("dim") = d;
    return result;
}

BlitzFun(1:8,c(2,2,2))

, , 1

     [,1] [,2]
[1,]  2.2  4.2
[2,]  3.2  5.2

, , 2

     [,1] [,2]
[1,]  6.2  8.2
[2,]  7.2  9.2


thanks
florian











On 18 December 2013 12:51, Dirk Eddelbuettel <edd at debian.org> wrote:

>
> Hi Florian,
>
> On 18 December 2013 at 11:12, Florian Oswald wrote:
> | I have a C++ class that I build and test without the help of Rcpp.
> |
> | I use Rcpp as an interface, inputting and outputting data from and to the
> | class. I'm stuck at the outputter. Ideally I would like to have this at
> the end
> | of my program:
> |
> | Rcpp::List Results = MyClass.ExportToR();
> |
> | where ExportToR is a method that creates an Rcpp::List from members of
> MyClass.
> | However, I'm unable to use components of Rcpp.h in my code; In
> particular, I'm
>
> If you want to use R in your own main, use  RInside  which makes this
> trivial. We ship it with several dozen examples.
>
> If you want to return a generic list structure, use the eg the STL type
> list
> (or, as you are using Blitz, maybe one of its containers).
>
> | unable to make this toy example work:
> |
> | #include <iostream>
> | #include <cstdlib>
> | #include <blitz/array.h>
> | #include <Rcpp.h>
> | #include <R.h>
> |
> | using namespace std;
> |
> | int main(int argc, char *argv[])
> | {
> |   Rcpp::IntegerVector d;
> |
> |   // Rcpp::List L; want to use
> |   // L to output results to R.
> |
> |  return EXIT_SUCCESS;
> | }
> |
> | I compile it with
> |
> | llvm-g++-4.2 -arch x86_64
> -I/Library/Frameworks/R.framework/Resources/include
> | -DNDEBUG -W -I/usr/local/include -I/usr/local/include
> -I"/Library/Frameworks/
> | R.framework/Versions/3.0/Resources/library/Rcpp/include"
> -L"/Library/Frameworks
> | /R.framework/Versions/3.0/Resources/library/Rcpp/lib/"
> -L"/Library/Frameworks/
> | R.framework/Versions/3.0/Resources/lib" export.cpp -lRcpp -lR -o  export
> |
> | which compiles, but produces a segfault.
>
> To be expected. R is its own main program, you cannot mix as you did. I
> suspect you may find RInside useful; it deploys all of Rcpp for parameter
> exchange.
>
> Cheers. Dirk
>
>
> | Thanks for any help!
> |
> | Florian
> |
> |
> |
> |
> |
> |
> |
> | ----------------------------------------------------------------------
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> | Rcpp-devel at lists.r-forge.r-project.org
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> --
> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
>
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