[Rcpp-devel] Testing for existence of named components

On 29/03/2012 18:33, Dirk Eddelbuettel wrote:

On 29 March 2012 at 19:12, Romain Francois wrote:
| Le 28/03/12 13:56, Ulrich Bodenhofer a ?crit :
|> Hi,
|>
|> My question is the following: is there any way of checking in
whether a
|> component of an Rcpp list (or vector) with a given name exists in this
|> list. If I simply try accessing a non-existing component, I get an
|> "index out of bounds" error. Trying to catch a possible exception did
|> not work either. I also browsed the Rcpp package source code, but
|> unfortunately I got lost. Sorry if this has been addressed on this
list
|> before. At least I googled in many different ways, but could not find
|> anything. Any ideas? Any help is gratefully appreciated!
|>
|> Thanks and best regards,
|> Ulrich
|
| Hello,
|
| I commited the has_element_called method on the Vector template
(vectors
| of all sorts, incl lists).

+1, but how about just calling it 'contains' rather
'has_element_called' ?

I think 'contains' would imply a value
in the vector rather than a name. The
extra typing might be worth avoiding
that confusion.

Pat

| For example:
|
| require(Rcpp)
| require(inline)
|
| fx<- cxxfunction( signature( x_ = "list" ), '
| List x(x_) ;
| bool has_foo = x.has_element_called( "foo" ) ;
| Rprintf( "has(foo) = %d\\n", has_foo ) ;
|
| bool has_bar = x.has_element_called( "bar" ) ;
| Rprintf( "has(bar) = %d\\n" , has_bar) ;
|
| return R_NilValue ;
| ', plugin = "Rcpp" )
|
| x<- list( foo = 2, bla = 1:10 )
| fx( x )
|
|
| For the curious amongst you, the code looks like this :
|
| /**
| * Does this vector have an element with the target name
| */
| bool has_element_called( const char* target ) const {
| SEXP names = RCPP_GET_NAMES(m_sexp) ;
| if( Rf_isNull(names) ) return false ;
| int n = Rf_length(names) ;
| for( int i=0; i<n; i++){
| if( !strcmp( target, CHAR(STRING_ELT(names, i)) ) ) return
| true ;
| }
| return false ;
| }
|
| It would be awesome if someone would contribute a unit test for this
| feature based on the inline snippet above.

I'll get to it.

Dirk

| Romain
|
|
|
| --
| Romain Francois
| Professional R Enthusiast
| +33(0) 6 28 91 30 30
| R Graph Gallery: http://addictedtor.free.fr/graphiques
| blog: http://romainfrancois.blog.free.fr
| |- http://bit.ly/xbKv0R : Crawling facebook with R
| |- http://bit.ly/v3WB8S : ... And now for solution 17, still using Rcpp
| `- http://bit.ly/uaQDGr : int64: 64 bit integer vectors for R
| _______________________________________________
| Rcpp-devel mailing list
| Rcpp-devel at lists.r-forge.r-project.org
| https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel