[R] Definition of generic function for subclasses

[Martin Morgan]

On 03/13/2012 04:34 AM, Alexander wrote:
> Hi,
> I am working on a project, which contains S4 classes and subclasses. Lets
> assume the following organisation:
> A: S4 Class
> B,C: inherit from A
> D,E,F,G: inherit from B
> H,I: inherit from C
>
> I want to define now a generic function, which returns me the name of the
> class. I can now write the function with "A" in the signature. Is there any

?class for this function

> reason to write the function for B,C, D,E,... with "B","C","D","E", .. in
> the signature ? I can imagine that it can become a mess if for example I

Implement the method at the lowest (highest?) level in the hierarchy as 
possible -- so on "A" only for the example of class.

> write a function for "A" and a special function for "I" (lets assume, I is
> the only exception).

If 'I' is somehow special then write a method for it alone

   setClass("A"); setClass("C", "A"); setClass("I", "C")

   setGeneric("cls", function(x, ...) standardGeneric("cls"))
   setMethod(cls, "A", function(x, ...) as.vector(class(x)))
   setMethod(cls, "I", function(x, ...) tolower(as.vector(class(x))))

and then

 > cls(new("C"))
[1] "C"
 > cls(new("I"))
[1] "i"

> Have you any best-work-pratice to share ?

Keep your class hierarchy simple and relevant to your actual problem.

Martin

>
> Thanks
> Alexander
>
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