Hi Edna --
Quoting Edna Bell <edna.bel...@gmail.com>:
I have put together a test class and methods
setClass("foo",representation(x="numeric"))
[1] "foo"
This creates an *S4* class which HAS A 'slot' x that is of type numeric.
setMethod("plot","foo",function(x,y,...)boxplot(x,...))
[1] "plot"
x <- rnorm(100)
class(x) <- "foo"
uh oh, this is creating an *S3* class that IS A numeric that has been
given the class name "foo". The S3 class 'foo' and S4 class 'foo' are
different. Note that you can make anything an S3 class
z=letters
class(z) <- "foo"
because S3 does not have any definition for what a 'foo' class is.
plot(x)
this 'works' but in my view should not -- the method is defined for
the S4 class, not for the S3 class.
y <- new("foo",x=rnorm(50))
Here you're creating an instance of the S4 class. S4 insists that
objects constructed as class 'foo' conform to the class specification
new("foo", x=letters)
Error in validObject(.Object) :
invalid class "foo" object: invalid object for slot "x" in class
"foo": got cl
ass "character", should be or extend class "numeric"
class(y)
[1] "foo"
My question is: should I have a "foo" function which sets the class
to "foo", please? or a sort of Validity checker, please?
I think normally one would have class "Foo" (capitalized; this is my
style & convention, others are free to do as they please) with
constructor
setClass("Foo", representation=representation(x="numeric"))
Foo <- function(x=numeric(), ...)
{
new("Foo", x=x, ...)
}
I'd normally also define a validity method with setValidity("Foo",
<etc>) if my class had constraints other than 'slot x has to be
numeric' (which is checked by the default validity method). Dispatch
on validity methods is different from on standard methods, as
explained in ?setValidity.
Hope that helps,
Martin
Thanks,
Edna Bell
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
