[Rcpp-devel] clarification of interaction between RInside and RcppEigen

[Stephen J. Barr]

Ah, I see the error. Please disregard this. I see how Rcpp::as works now.

Best,
Stephen

On Tue, Aug 7, 2012 at 2:08 PM, Stephen J. Barr <stephenjbarr at gmail.com>wrote:

> Hello again,
>
> I am just trying to straighten this out. Say I want to have the exact same
> random matrix in C++ as I do in R using rnorm. Is what I am doing below on
> the right track?
>
> Thanks,
> Stephen
>
> //
> // Stephen J. Barr
> //   - trying to combine RInside and Eigen
>
> #include <RInside.h>
> #include <Eigen/Dense>
>
>
> using namespace Eigen;
> using namespace std;
>
>
>
> int main(int argc, char *argv[]) {
>
>     RInside R(argc, argv);
>     int nrow = 3;
>     int ncol = 4;
>     R.parseEvalQ("set.seed(1)");
>     MatrixXd mymat = MatrixXd(nrow, ncol);
>     R.parseEvalQ("MYMAT = matrix(rnorm(3*12),nrow=3)");
>     const Map<MatrixXd> mymat(as<Map<MatrixXd>>(MYMAT));
>
>
>     exit(0);
>
> }
>
>
> On Tue, Aug 7, 2012 at 11:32 AM, Stephen J. Barr <stephenjbarr at gmail.com>wrote:
>
>> Thank you Dirk and also Douglas. This definitely helps. I think I can get
>> this going. Thank you so much for the quick replies.
>>
>> Best,
>> Stephen
>>
>>
>> On Tue, Aug 7, 2012 at 11:29 AM, Dirk Eddelbuettel <edd at debian.org>wrote:
>>
>>>
>>> Hi Stephen,
>>>
>>> On 7 August 2012 at 10:55, Stephen J. Barr wrote:
>>> | Greetings,
>>> |
>>> | I am new to Rcpp, RInside and the entire family of related packages. I
>>> am
>>> | experienced with R and also C++ using Eigen but I have never combined
>>> the two
>>> | before.
>>>
>>> You are in a good starting position.
>>>
>>> | I would like to create a matrix using R and then play with it using
>>> | Eigen. From what I have read so far, it seems like I can use RInside
>>> to create
>>> | an Rcpp::NumericMatrix.
>>>
>>> That works. Even one of the very oldest examples (rinside_sample1.cpp)
>>> does
>>> something related with a Rcpp::NumericMatrix (eg creates one and passes
>>> it around).
>>>
>>> | My question is this: to transform a matrix from a Rcpp::NumericMatrix
>>> to an
>>> | Eigen MatrixXd, do I use RcppEigen? Or is RcppEigen only for calling
>>> C++/Eigen
>>> | from R and not the other way around?
>>>
>>> I think I have an idea as to what you are asking. I think it may help to
>>> step
>>> back for a second and try to imagine the big picture:
>>>
>>> a) Rcpp helps us with the interface defined by .Call:
>>>
>>>      SEXP .Call(string somefuncname, SEXP arg1, SEXP arg2, ...)
>>>
>>>    so everthing going in and out is a SEXP type.
>>>
>>> b) RInside lets you interchange with an embedded R process, again talking
>>>    SEXPs.
>>>
>>> c) Packages like RcppEigen provide wrappers to and from SEXPs.
>>>
>>> So if you don't need a Rcpp::NumericMatrix, don't create one.  Create an
>>> Eigen matrix, and use RcppEigen's wrappers to pass it throught the SEXP
>>> interfaces.  That should work just fine with RInside as well.
>>>
>>> You will have to expand the RInside Makefile to point to the RcppEigen
>>> headers as well, and then it should just work.
>>>
>>> Hope this helps,  Dirk
>>>
>>>
>>> | Thanks,
>>> | Stephen
>>> |
>>> | ----------------------------------------------------------------------
>>> | _______________________________________________
>>> | Rcpp-devel mailing list
>>> | Rcpp-devel at lists.r-forge.r-project.org
>>> |
>>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>>> --
>>> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
>>>
>>
>>
>
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