[Rcpp-devel] Resurrecting rinside_sample9.cpp ?

[Dirk Eddelbuettel]

On 23 July 2014 at 14:41, Christian Authmann wrote:
| Hello,
| 
| I'm trying to run user provided R scripts from within my C++ 
| applications using RInside. I have a large amount of data (larger than 
| RAM) the R script can potentially access, so it's impossible to provide 
| it all in a variable - I'd need to provide a callback so the R script 
| can request the data it needs.
| 
| The idea is to have a function similar to sample9 (minus the bug[1])
| 
| Rcpp::NumericVector getdata(int id) {
| 	Rcpp::NumericVector vec();
| 	// ...
| 	return vec;
| }
| 
| and make it available like:
| 
| RInside R;
| R["getdata"] = Rcpp::InternalFunction( &getdata );
| 
| 
| 
| As hinted in sample9, Rcpp::InternalFunction apparently really is 
| broken. Instantiating it gives compiler errors very similar to those 
| everyone got in Rcpp 0.11.0. [2]
| 
| I've updated both Rcpp and RInside to the latest release version, but 
| the errors remain.

I was about to say that need Github versions of both as the fixes went in
pretty recently:

  edd at max:~$ cd git/rinside/inst/examples/standard/
  edd at max:~/git/rinside/inst/examples/standard$ ./rinside_sample9 
  hello( 'world') =  hello world
  edd at max:~/git/rinside/inst/examples/standard$ 

but then I realized that I am seemingly behind one commit -- the very latest
fix of making rinside_sample9.cpp use a std::string.  

So apologies -- I blame my recent traveling and will update the repo this
evening.  For now, the repaired rinside_sample9.cpp is included below. You
will need Rcpp from Github.

| Am I doing something wrong, or is this feature fundamentally broken? Is 
| there anything I can do to fix it?

Worst case you can always do what Github user 'omazapa' did and fix it in
Rcpp and/or RInside as needed :)

More seriously, the brokenness only applied to Rcpp::InternalFunction which
was more or less deprecated as Rcpp::Function worked.
 
| Or are there other ways to add a function to the R script's environment? 
| I've read of plenty of ways using Rcpp, but those only seem to apply 
| when developing R packages. I could provide an R package, include it 
| from the RInside script and thus have a custom function; but the R 
| package would be separate from my application and wouldn't have access 
| to the data it needs to provide.

There are lots examples that ship with RInside; some use functions -- maybe
these can provide an idea.

Otherwise, "it is just R" as we embed the interpreter.  Whatever you could do
with R as is you should be able to do with RInside.  Which works both ways --
thing that you can't do easily with R will also be hard for RInside.
 
| Or should I just install older RInside/Rcpp packages where it still 
| compiled, and work with those for now?

That is also always an option.

Dirk

// -*- mode: C++; c-indent-level: 4; c-basic-offset: 4;  tab-width: 8; -*-
//
// Simple example showing how expose a C++ function -- no longer builds
//
// Copyright (C) 2010 Dirk Eddelbuettel and Romain Francois

#include <RInside.h>                    // for the embedded R via RInside

// a c++ function we wish to expose to R
std::string hello( std::string who ){
    std::string result( "hello " ) ;
    result += who ;
    return result;
} 

int main(int argc, char *argv[]) {

    // create an embedded R instance
    RInside R(argc, argv);               

    // expose the "hello" function in the global environment
    R["hello"] = Rcpp::InternalFunction( &hello ) ;
   
    // call it and display the result
    std::string result = R.parseEvalNT("hello(\"world\")") ;
    std::cout << "hello( 'world') =  " << result << std::endl ; 

    exit(0);
}





| 
| 
| 
| [1] return result.c_str(); returns a dangling pointer, since result is 
| destroyed before returning.
| [2] according to 
| http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2014-March/007290.html
| 
| -- 
| Christian Authmann
| Philipps-Universität Marburg
| Fachbereich Mathematik und Informatik
| AG Datenbanksysteme
| Hans-Meerwein-Straße
| D-35032 Marburg
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-- 
http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org