[Rcpp-devel] Testing for existence of named components

[Romain Francois]

Le 29/03/12 19:51, Patrick Burns a écrit :
> 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

I don't mind if the name changes, but Pat has a point.

Romain

>> | 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
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>> | blog: http://romainfrancois.blog.free.fr
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>> | |- http://bit.ly/v3WB8S : ... And now for solution 17, still using Rcpp
>> | `- http://bit.ly/uaQDGr : int64: 64 bit integer vectors for R
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>>
>


-- 
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