>>>>> Fox, John
>>>>> on Fri, 21 Dec 2018 16:16:40 +0000 writes:
> Dear Martin,
> Since no one else has picked up on this, I’ll take a crack
> at it:
Thank you, John
> The proposal is to define the S3 class of model-frame
> objects as c(“model.frame”, “data.frame”) (not the formal
> class of these objects, even though this feature was
> coincidentally introduced in S4). That’s unlikely to do
> harm, since model frames would still “inherit” data.frame methods.
Well, sure, "in theory".
My fear is different -- and I think for good reasons :
IIRC, I've seen slides of a talk by a well respected R
community member where they advertized -- IIRC, even as example
of good R programming -- to use
switch(class(obj)[1],
"foo" = { .... some things .... },
"bar" = { .... other things .... },
.....
stop("invalid class ", class(obj)[1])
)
and I have seen many package authors use analogously "broken" R
code
if(class(obj) == "foo") { # deal with "foo" ...
....
} else if(class(obj) == "bar") {
...
} else .....
all of which will fail if users of that code (including other
package writers) decide to extend that S3 class using a
length(class(.)) >= 2 ....
Now, with Bill Dunlap's findings about S-plus 8.3, namely that
it does not contain a *single* model.frame method,
I'd rather tend to only fix formula.data.frame()
Martin
> It's possible that some packages rely on current
> data.frame methods that are eventually superseded by
> specific model.frame methods or do something peculiar with
> the class of model frames, so as far as I can see, one
> can’t know whether problems will arise before trying it.
> I hope that helps, John
> -------------------------------------------------
> John Fox, Professor Emeritus McMaster University
> Hamilton, Ontario, Canada Web:
> http::/socserv.mcmaster.ca/jfox
>> On Dec 21, 2018, at 2:51 AM, Martin Maechler
>> <maech...@stat.math.ethz.ch> wrote:
>>
>>>>>>> William Dunlap via R-devel on Thu, 20 Dec 2018
>>>>>>> 15:09:56 -0800 writes:
>>
>>> When formula() is applied to the output of model.frame()
>>> it ignores the formula in the model.frame's 'terms'
>>> attribute:
>>
>>>> d <- data.frame(A=log(1:6), B=LETTERS[rep(1:2,c(2,4))],
>>>> C=1/(1:6),
>>> D=rep(letters[25:26],c(4,2)), Y=1:6)
>>>> m0 <- model.frame(data=d, Y ~ A:B) formula(m0)
>>> Y ~ A + B
>>>> `attributes<-`(terms(m0), value=NULL)
>>> Y ~ A:B
>>
>>> This is in part because model.frame()'s output has class
>>> "data.frame" instread of c("model.frame","data.frame"),
>>> as SV4 did, so there are no methods for model.frames.
>>
>>> Is there a reason that model.frame() returns a
>>> data.frame with extra attributes but no special class or
>>> is it just an oversight?
>>
>> May guess is "oversight" || "well let's keep it simple"
>> Do you (all readers) see situation where it could harm
>> now (with the 20'000 packages on CRAN+BIoc+...) to do as
>> SV4 (S version 4) has been doing?
>>
>> I'd be sympathetic to class()ing it. Martin
>>
>>> Bill Dunlap TIBCO Software wdunlap tibco.com
>>
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