Hi Chris,
I personally found the documentation rather...indigestible. At least 3
years ago when I developed my R package. It seems they have nicely
improved this part of the documentation though.
I'm not an expert at all, but at least you will have the point of view
of a beginner.
First, in your C or C++ file, redefine the type of you main function to
SEXP so it returns an R-type object. Then change your object(s) to SEXP
to be compatible with R. Don't forget to protect your variable(s) (and
unprotect it at the end). (For C++ only, encapsulate your function with
'extern "C"'). Also add this three headers in your file :
#include <R.h>
#include <Rinternals.h>
#include <Rdefines.h>
Run R CMD SHLIB on your C/C++ file. You should obtain a .so file.
In R, use dyn.load to load the .so file. Then you can use .Call.
////////////////////////////////////////////////////////////////////////////
Here is an example :
testC.c :
#include <R.h>
#include <Rinternals.h>
#include <Rdefines.h>
//extern "C" { // for C++ only
SEXP myCfunction (SEXP myList) //this function return a SEXP object
{
SEXP myResults; //definition of a new SEXP object, usable by R
double tmp = 0;
PROTECT(myResults = allocVector(REALSXP, 1)); //don't forget to
protect your variable !
for (int i=0; i<GET_LENGTH(myList); i++)
{
tmp = tmp + NUMERIC_VALUE(VECTOR_ELT(myList,i)); // refer
to Rinternals.h for a complet list of types
}
REAL(myResults)[0] = tmp;
UNPROTECT(1); //free the variable
return(myResults);
}
//} // end of extern "C"
Then run R CMD SHLIB testC.c
In R :
dyn.load("testC.so")
myList=list(1,2,3,4,5,6)
myResultsFromC <- .Call("myCfunction", myList=myList)
myResultsFromC
[1] 21
I hope this help.
Eloi
On 12-04-15 12:11 AM, Prof Brian Ripley wrote:
On 15/04/2012 05:22, chris90nz wrote:
Hi,
I am currently stuck on the following problem: I have a matrix where
each
element is a list of numbers of differing lengths. I am wondering
what would
be the best way to send this to my C function using .C?
Follow the documentation ....
This is not the list for discussing compiled code (see the posting
guide), nor have you told us what you tried. But in fact there is
only one way to do this, and ?.C and 'Writing R Extensions' explain it
to you.
I have no idea why you would have 'a list of numbers of differing
lengths'. First, what is the length of a number? Second, why not
store numbers in numeric vectors? An example (as required by the
posting guide) would have helped compensate for an imprecise description.
Cheers,
Chris
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Eloi Mercier
Bioinformatics PhD Student, UBC
Paul Pavlidis Lab
2185 East Mall
University of British Columbia
Vancouver BC V6T1Z4
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