[R] Inheriting from factors + co.
Torsten.Steuernagel at gmx.de
Wed Feb 25 11:43:34 CET 2004
On 25 Feb 2004 at 10:00, Uwe Ligges wrote:
> So you are going to handle/mix the S4 class like/with S3 classes? Hmm.
Yes, and there is the problem. With S4 classes, it works. Now I would
expect that is(factor(S3object, "ANY") will be FALSE for factor and any
other S3 class, but is(S3object, "ANY") always gives TRUE.
> It can be either of class "myclass" or of class "factor". I'd define a
> separate explicit slot for such a class:
It is of class "myclass" but it should inherit from "factor" by the .Data
part if I specify a factor. That's what it does with S4 classes:
my1 <- new("myclass", 1:10)
class(my1) # "myclass"
is.numeric(my1) # TRUE
my2 <- new("myclass", "abc")
class(my2) # "myclass"
is.character(my2) # TRUE
In those cases the object actually is a numeric or a character and thus
can be treated accordingly.
> setClass("myclass", representation(mainSlot = "ANY",
> x = "numeric", y = "numeric"))
That works, of course. But that's not what I'm looking for. This requires
using the slot explicitly (not impossible, but I'd really prefer to have it in
the .Data part). One main drawback is that R just doesn't accept S3
classes as .Data part:
It creates a new class (although a warning is issued) and also extends
from "factor" but doesn't create the .Data slot. That's also the reason
why my second approach with setClassUnion() doesn't work as soon as
an S3 class is part of the union. I just don't understand why S3 classes
in explicit slots work perfectly well whereas it seems impossible to have
them in the .Data slot.
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