Oliver, For an example of moving averages, take a look at the C source of the xts and TTR packages. The sources are browsable on R-forge.
In short, REAL etc are functions to extract the data of an SEXP. They need to match the types coming in. So your C needs to check the type and branch accordingly. It is all in the guide as well as in working example code in R sources as well as many hundreds of package sources. You have access to it all, so spend the time just reading the sources is my recommendation. Best, Jeff Jeffrey Ryan | Founder | jeffrey.r...@lemnica.com www.lemnica.com On Jun 3, 2011, at 3:19 PM, oliver <oli...@first.in-berlin.de> wrote: > On Fri, Jun 03, 2011 at 11:14:39AM -0500, Douglas Bates wrote: >> On Fri, Jun 3, 2011 at 5:17 AM, oliver <oli...@first.in-berlin.de> wrote: >>> Hello, >>> >>> I'm implementing a package (C-extension), >>> where one function gets data and a function >>> that needs to be applied to the data. >>> >>> I want to apply the function to (parts of) >>> the data on the C-side. >>> >>> 1) how do I apply a function (given via SEXP) to data >>> 2) how do I select parts of the data (also provided via SEXP)? >> >> Not to be facetious but you begin by reading the "Writing R Extensions" >> manual. > > I already read inside it. > If there would be no question open i would not have registered to this > mailing list > and woulod not have asked that question. > Obviously my question was not answered in the "Writing R Extensions", > so if you can give me a hint this would be nice. > > >> >> An alternative is to read the vignette Rcpp-Introduction available as >> http://dirk.eddelbuettel.com/code/rcpp/Rcpp-introduction.pdf and soon > > I use C, not C++. > > But maybe it helps too. > > I already created my own package with R and C successfully some days ago. > > But so far I did not used fucntion pointers coming in via SEXP parameters. > > And that was my specific question. > > > > >> to be in The R Journal. They show an explicit example of apply in >> compiled code (C++ using the Rcpp structures, in their case). > > > As just mentioned: I already created successfully a C-extension for R. > > But I would like to know, how to call a function that I get via > SEXP as parameter. How can I find out the function definition, > for example the arity of the function and which arguments > a function uses. > > The problem is, that the C-standard (at least the first ANSI-C standard) > does not guarantee portability for C-pointers. > To be portable, for example the function pointer you use must > definitely be of same type as the function you use. > > So I need to know how I can use the SEXP-function pointers. > > > To be more concrete, this is how my function's API looks like > at the moment: > > SEXP movapply( SEXP data, SEXP width, SEXP func ) > { > /* some code */ > > return ( result ); > } > > > > data will be vector or list or matrix > width will be int value (I think vector of length 1) > func will be a function pointer of the type that is given as argument > > I don't know on which kind of pointer to cast. > I think I will cast to a pure C-type, but then all data also must > match to the function definition. > > What if the function wants to work on integer, but the data is double? > > Somehow this must be handled, and I think the experts here can just point me > directly to some kind of docs or maybe older postinmgs here, which explain > this? > > > Ciao, > Oliver > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
