Rcpp 0.7.2

January 13, 2010
By

(This article was first published on Romain Francois, Professional R Enthusiast, and kindly contributed to R-bloggers)

Rcpp 0.7.2 is out, checkout Dirk’s blog for details

selected highlights from this new version:

character vectors

if one wants to mimic this R code in C

> x <- c( "foo", "bar" )

one ends up with this :

SEXP x = PROTECT( allocVector( STRSXP, 2) ) ;
SET_STRING_ELT( x, 0, mkChar( "foo" ) ) ;
SET_STRING_ELT( x, 1, mkChar( "bar" ) ) ;
UNPROTECT(1) ;
return x ;

Rcpp lets you express the same like this :

CharacterVector x(2) ;
x[0] = "foo" ; 
x[1] = "bar" ;

or like this if you have GCC 4.4 :

CharacterVector x = { "foo", "bar" } ;

environments, functions, ...

Now, we try to mimic this R code in C :

rnorm( 10L, sd = 100 )

You can do one of these two ways in Rcpp :

Environment stats("package:stats") ;
Function rnorm = stats.get( "rnorm" ) ;
return rnorm( 10, Named("sd", 100 ) ) ;

or :

Language call( "rnorm", 10, Named("sd", 100 ) ) ;
return eval( call, R_GlobalEnv ) ;

and it will get better with the next release, where you will be able to just call call.eval() and stats["rnorm"].

Using the regular R API, you'd write these liks this :

SEXP stats = PROTECT( R_FindNamespace( mkString("stats") ) ) ;
SEXP rnorm = PROTECT( findVarInFrame( stats, install("rnorm") ) ) ;
SEXP call  = PROTECT( LCONS( rnorm, CONS(ScalarInteger(10), CONS(ScalarReal(100.0), R_NilValue)))) ;
SET_TAG( CDDR(call), install("sd") ) ;
SEXP res = PROTECT( eval( call, R_GlobalEnv ) );
UNPROTECT(4) ;
return res ;

or :

SEXP call  = PROTECT( LCONS( install("rnorm"), CONS(ScalarInteger(10), CONS(ScalarReal(100.0), R_NilValue)))) ;
SET_TAG( CDDR(call), install("sd") ) ;
SEXP res = PROTECT( eval( call, R_GlobalEnv ) );
UNPROTECT(2) ;
return res ;

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