[Rcpp-devel] Testing for existence of named components

[Dirk Eddelbuettel]

On 29 March 2012 at 19:12, Romain Francois wrote:
| Le 28/03/12 13:56, Ulrich Bodenhofer a écrit :
| > 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' ?

| 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
| 
| 
| 
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