Hi,
Le 14/06/10 05:38, R_help Help a écrit :
Hi,
I have a doubt regarding passing large data frame into Rcpp. If we
consider the following function
foo(SEXP myframe) {
RcppFrame&fr_ref = (RcppFrame&) myframe;
}
Somehow seems to work without a need to call a constructor and thus
causes copy of large data frame to RcppFrame object.
This is very wrong code, you are just getting lucky about the internal
representation of RcppFrame.
Consider:
require( Rcpp )
require( inline )
inc <- '
class Foo{
public:
Foo( SEXP x) : y(5), xx(x) {
Rprintf( "hello" ) ;
}
Foo( ) : y(6), xx(R_NilValue) {
Rprintf( "hello from default" );
}
inline SEXP gety(){
return IntegerVector::create( y ) ;
}
private:
int y ;
SEXP xx ;
} ;
'
code <- '
Foo& foo = (Foo&) x ;
return foo.gety() ;
'
df <- data.frame( x = 1:5, y = 1:5 )
fx <- cxxfunction( signature( x = "data.frame" ), code, include = inc,
plugin = "Rcpp" )
I get :
> fx( df )
[1] 35966160
> fx( df )
[1] 35966160
Using C++ cast "static_cast", the compiler would tell you the error.
file10d63af1.cpp: In function ‘SEXPREC* file10d63af1(SEXPREC*)’:
file10d63af1.cpp:49: error: invalid static_cast from type ‘SEXPREC*’ to
type ‘Foo&’
make: *** [file10d63af1.o] Error 1
ERROR(s) during compilation: source code errors or compiler
configuration errors!
However, you can
see that the code is not safe.
It is more than "not safe", it is just plain wrong.
there's no guarantee that myframe is a
data frame. This is my first question, is there any way to check type
of the input SEXP? Or is there any better way to do this?
RcppFrame is a class of what we call the "classic" api, which indeed is
largely inefficient because it copies data all the time.
The new api, and in particular the class Rcpp::DataFrame is much more
efficient. For example the constructor
Rcpp::DataFrame( SEXP )
will not make a copy of the SEXP you pass in.
You can find example code of Rcpp::DataFrame in the unit test:
> system.file( "unitTests", "runit.DataFrame.R", package = "Rcpp" )
Secondly, I'm wondering why the POSIXct column in my data frame
appears as double when I pass a data frame as an argument into a
function or when I read it out from global environment map? Is there
anyway to ensure it appears as RcppDatetime? Thank you.
Robert
Someone else will pick this up.
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
|- http://bit.ly/98Uf7u : Rcpp 0.8.1
|- http://bit.ly/c6YnCi : graph gallery collage
`- http://bit.ly/bZ7ltC : inline 0.3.5
_______________________________________________
Rcpp-devel mailing list
[email protected]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
