[R] Method for $

Fri Nov 18 20:07:56 CET 2005

Berton, thanks for your code, it does work on my problem. However, I do want 
the $ do work the extraction, and it does if I do it right (see answer from 
Duncan Temple Lang).
Regards, Ulrike

---------- Original Message ----------- 
From: Berton Gunter <gunter.berton at gene.com> 
To: "'Uwe Ligges'" <ligges at statistik.uni-dortmund.de>, "'Ulrike Grömping'" 
<groemp at tfh-berlin.de> 
Cc: <r-help at stat.math.ethz.ch> 
Sent: Fri, 18 Nov 2005 09:42:12 -0800 
Subject: RE: [R] Method for $

> I believe that a  recommended S4 convention is simply to write methods for 
> slot extraction with the same name as the slot. Thus, for an object,x of 
> class 'myclass' 
> 
> slotname(x) 
> 
> would give x at slotname. This is a more natural interface than either @ or $ 
> (and I am not sure that methods for $ can be defined due to S3/S4 class 
> consistency details). 
> 
> Obviously, it is trivial, but a bit tedious, to manually write such methods 
> for any class you care to. However, I wrote a small generator function that 
> automatically generates the slot extraction methods for any class if you 
> wish to do things this way. I just run this right after I've define a new 
> class,'myclass', to generate slot access methods by: slotget('myclass') 
> 
> The code is below. I would appreciate feedback on any errors or suggestions 
> for improvement. 
> 
> Cheers, 
> 
> -- Bert Gunter 
> Genentech Non-Clinical Statistics 
> South San Francisco, CA 
> 
> slotGet<-function(x,where=topenv()) 
> #automatically generates accessor and replacement methods for class x 
> { 
>     if(!isClass(x,where=where))stop(paste('Class',x,'not found')) 
>     slots<-slotNames(getClass(x,where=where)) 
>    for(slt in slots){ 
>              ## slot accessor 
>        fun<-function(object)NULL 
>           if(!isGeneric(slt,where=where)){ 
>                if(exists(slt,where=where,mode="function")) 
>                     fun<-get(slt,pos=where,mode="function") 
>               else body(fun)<-substitute(standardGeneric(slt)) 
>                setGeneric(slt,fun,where=where) 
>          } 
>           if(!existsMethod(slt,x,where=where)){ 
>             body(fun)<-substitute(object at slt) 
>             setMethod(slt,x,fun,where=where) 
>        } 
>     } 
>     invisible() 
> } 
> 
> > -----Original Message----- 
> > From: r-help-bounces at stat.math.ethz.ch 
> > [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Uwe Ligges 
> > Sent: Friday, November 18, 2005 8:46 AM 
> > To: Ulrike Grömping 
> > Cc: r-help at stat.math.ethz.ch 
> > Subject: Re: [R] Method for $ 
> > 
> > Ulrike Grömping wrote: 
> > 
> > > Dear R experts, 
> > > 
> > > I have defined a class "myclass" and would like the slots 
> > to be extractable 
> > > not only by "@" but also by "$". I now try to write a 
> > method for "$" that 
> > > simply executes the request object at slotname, whenever someone calls 
> > > object$slotname for any object of class "myclass". 
> > > I don't manage to find out how I can provide this function 
> > with "slotname", 
> > > so that one and the same function works for any arbitrary 
> > slotname a user 
> > > might choose. 
> > > 
> > > I have tried 
> > > 
> > > setMethod("$", signature(x="myclass"), function(x,slotname){ 
> > >  x at slotname 
> > >  } 
> > > ) 
> > 
> > 
> > Ulrike, 
> > 
> > what about (untested!): 
> > slot(x, slotname) 
> > 
> > Best wishes from Dortmund and Lena, 
> > Uwe Ligges 
> > 
> > 
> > > This produced the error message: 
> > > In method for function "$": expanding the signature to 
> > > include omitted arguments in definition: name = "missing" 
> > > Error in rematchDefinition(definition, fdef, mnames, 
> > fnames, signature) : 
> > >         methods can add arguments to the generic only if 
> > '...' is an argument 
> > > to the generic 
> > > 
> > > My searches for a solution of this problem have not been 
> > successful. Can 
> > > someone help? 
> > > 
> > > Thanks and regards, 
> > > Ulrike Grömping, Berlin 
> > > 
> > > ______________________________________________ 
> > > R-help at stat.math.ethz.ch mailing list 
> > > https://stat.ethz.ch/mailman/listinfo/r-help 
> > > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html 
> > 
> > ______________________________________________ 
> > R-help at stat.math.ethz.ch mailing list 
> > https://stat.ethz.ch/mailman/listinfo/r-help 
> > PLEASE do read the posting guide! 
> > http://www.R-project.org/posting-guide.html 
> > 
------- End of Original Message -------