[Rcpp-devel] Rcpp sugar

[Romain Francois]

Hello,

Initially motivated by Doug's question: 
http://article.gmane.org/gmane.comp.lang.r.rcpp/412

and drafted quickly in : http://article.gmane.org/gmane.comp.lang.r.rcpp/422

I've added some code in Rcpp that I call "Rcpp sugar" (another name I 
had in mind was "Rcpp plasma". I like sugar because what this does is to 
add some syntactic sugar so that Rcpp code looks more like R code.

So now we can use "any" and "all" with binary operators <,>,<=,>=,!=,== 
on Rcpp vectors.

Here is one random example from the unit test suite:

test.sugar.all.less.or.equal <- function( ){

	fx <- cxxfunction( signature( x = "numeric", y = "numeric" ), '
	
		NumericVector xx(x) ;
		NumericVector yy(y) ;
		
		return all( xx <= yy ) ;
	
	', plugin = "Rcpp" )
	
	checkTrue( fx( 1, 1 ) )
	checkTrue( ! fx( 1:2, c(1,1) ) )
	checkTrue( fx( 0, 1 ) )
	checkTrue( ! fx( 1, 0 ) )
	checkTrue( is.na( fx( NA, 1 ) ) )
	
}


The difference between the Rcpp code:

all( xx <= yy )

and the R code

all( xx <= yy )


is that R would first allocate the logical vector resulting from the 
expression "xx <= yy" and then call all.

Rcpp::all does not need to allocate the logical vector, so will be more 
efficient.

This is the tip of the iceberg of what Rcpp::sugar could be, and uses a 
version of expression templates (e.g. see armadillo or Blitz).

Much more could be done, but this will get complicated to code at some 
point. So I'm not sure yet if I will or if I will wait for contributions 
or sponsorship, etc ...

See other examples in the test files that contain the word "sugar" :

 > list.files( system.file( "unitTests", package = "Rcpp" ), full = T, 
pattern = "sugar" )

Romain


-- 
Romain Francois
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http://romainfrancois.blog.free.fr
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