[Rcpp-devel] Testing for existence of named components

[Patrick Burns]

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 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' ?

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
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-- 
Patrick Burns
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