[Rcpp-devel] Turning a vector into a matrix

Fri May 31 12:28:28 CEST 2013

Romain,

Perhaps I now see the light at the end of the tunnel (hope it is not a train comming against me!): If I understand this correctly, the following

> template <int RTYPE>
> Matrix<RTYPE> vec2matrix2(Vector<RTYPE> x, int nrow, int ncol) {
>    return Matrix<RTYPE>(nrow, ncol, x.begin()); }

should do the dispatching properly if I call vec2matrix2 from a c++ function. Right? And all the other bells and whistles are merely to be able to call the function from R?

Cheers
Søren

-----Original Message-----
From: Romain Francois [mailto:romain at r-enthusiasts.com] 
Sent: 31. maj 2013 11:37
To: Søren Højsgaard
Cc: rcpp-devel at lists.r-forge.r-project.org
Subject: Re: [Rcpp-devel] Turning a vector into a matrix

Ah ok, so you want to use this from R, I would suggest to Rcpp::export a dispatcher, something like this:

#include <Rcpp.h>
using namespace Rcpp ;

// the template
template <int RTYPE>
Matrix<RTYPE> vec2matrix__impl(Vector<RTYPE> x, int nrow, int ncol) {
   return Matrix<RTYPE>(nrow, ncol, x.begin()); }

// the exported dispatcher,used from R
// [[Rcpp::export]]
SEXP vec2matrix(SEXP x, int nrow, int ncol){
     switch( TYPEOF(x) ){
         case REALSXP: return vec2matrix__impl( NumericVector(x), nrow, ncol ) ;
         case INTSXP:  return vec2matrix__impl( IntegerVector(x), nrow, ncol ) ;
         // ... add other cases you want to handle
     default:
         return R_NilValue ;
         // .. or do whatever
     }
}

/*** R
     vec2matrix( 1:10, 2, 5 )
     vec2matrix( rnorm(10), 2, 5 )
***/

Romain

Le 31/05/13 11:30, Søren Højsgaard a écrit :
> Romain,
>
> I actually already tried this in my file util.cpp but can't get it to work:
>
> #include <Rcpp.h>
>
> using namespace Rcpp;
>
> // [[Rcpp::export]]
> NumericMatrix vec2matrix(NumericVector x, int nrow, int ncol) {
>    return NumericMatrix(nrow, ncol, x.begin()); }
>
> // [[Rcpp::export]]
> template <int RTYPE>
> Matrix<RTYPE> vec2matrix2(Vector<RTYPE> x, int nrow, int ncol) {
>    return Matrix<RTYPE>(nrow, ncol, x.begin()); }
>
> Any thoughts?

Don't Rcpp::export templates.

> Søren
>
>
>
>> Rcpp::sourceCpp('./util.cpp')
> g++ -m64 -I"C:/programs/R/current/include" -DNDEBUG     -I"C:/programs/R/current/library/Rcpp/include"  -I"d:/RCompile/CRANpkg/extralibs64/local/include"     -O2 -Wall  -mtune=core2 -c util.cpp -o util.o util.cpp: In function 'SEXPREC* sourceCpp_50379_vec2matrix2(SEXP, SEXP, SEXP)': util.cpp:75:12: error: 'RTYPE' was not declared in this scope util.cpp:75:17: error: template argument 1 is invalid util.cpp:75:21: error: invalid type in declaration before '=' token util.cpp:75:44: error: could not convert template argument 'RTYPE' to 'int' util.cpp:75:53: error: no matching function for call to 'as(SEXPREC*&)' util.cpp:75:53: note: candidate is: C:/programs/R/current/library/Rcpp/include/Rcpp/as.h:125:29: note: template<class T> T Rcpp::as(SEXP) util.cpp:78:5: error: a template declaration cannot appear at block scope util.cpp:79:5: error: expected ';' before 'return' util.cpp:75:19: warning: unused variable 'x' [-Wunused-variable] util.cpp:76:9: warning: unused variable 'nro
 w' [-Wunu
sed-variable] util.cpp:77:9: warning: unused variable 'ncol' [-Wunused-variable] make: *** [util.o] Error 1
> Error in Rcpp::sourceCpp("./util.cpp") :
>    Error 1 occurred building shared library.
>
>
>
>
>
>
> -----Original Message-----
> From: rcpp-devel-bounces at lists.r-forge.r-project.org 
> [mailto:rcpp-devel-bounces at lists.r-forge.r-project.org] On Behalf Of 
> Romain Francois
> Sent: 31. maj 2013 11:22
> To: rcpp-devel at lists.r-forge.r-project.org
> Subject: Re: [Rcpp-devel] Turning a vector into a matrix
>
> Hello Søren,
>
> This is easy templating:
>
> template <int RTYPE>
> Matrix<RTYPE> vec2matrix(Vector<RTYPE> x, int nrow, int ncol) {
> 	return Matrix<RTYPE>(nrow, ncol, x.begin()); }
>
> will work for NumericVector, IntegerVector, CharacterVector, ...
>
> Romain
>
> Le 31/05/13 11:08, Søren Højsgaard a écrit :
>> Dear all,
>>
>> Dirk: Thanks for the reply :).
>>
>> I shall dare to ask a "bonus question": I've played around with templating so that I get the right output type. I know (thanks to an earlier reply by Romain) how to do so using SEXP's but if I am constructing a utility function to be used on c++ objects, I can't that to work. What I am after should mimic the following such that the output type is determined by the input type:
>>
>> NumericMatrix vec2matrix(NumericVector x, int nrow, int ncol) {
>>     return NumericMatrix(nrow, ncol, x.begin()); }
>>
>> IntegerMatrix vec2matrix(IntegerVector x, int nrow, int ncol) {
>>     return IntegerMatrix(nrow, ncol, x.begin()); }
>>
>> Any help would be more than welcome.
>>
>> Best regards
>> Søren
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: Dirk Eddelbuettel [mailto:edd at debian.org]
>> Sent: 31. maj 2013 03:01
>> To: Søren Højsgaard
>> Cc: rcpp-devel at r-forge.wu-wien.ac.at
>> Subject: Re: [Rcpp-devel] Turning a vector into a matrix
>>
>>
>> Soren,
>>
>> You missed the most appropriate constructor:
>>
>>       template <typename Iterator>
>>       Matrix( const int& nrows_, const int& ncols, Iterator start ) ;
>>
>> With that we just do this:
>>
>>     R> Rcpp::sourceCpp('/tmp/soren.cpp')
>>     R> soren(1:4,2,2)
>>          [,1] [,2]
>>     [1,]    1    3
>>     [2,]    2    4
>>     R>
>>
>> and the file soren.cpp is below.
>>
>> Dirk
>>
>>
>> #include <Rcpp.h>
>>
>> using namespace Rcpp;
>>
>> // [[Rcpp::export]]
>> NumericMatrix soren(NumericVector x, int n, int k) {
>>     return NumericMatrix(n, k, x.begin()); }

--
Romain Francois
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