[Rd] formula(model.frame(..)) is misleading

[William Dunlap]

I don't have a copy of SV4 (or SV3, where model.frame was introduced), but
S+ 8.3 (based on SV4) puts the class "model.frame" on model.frame()'s
return value but has no methods (in the default packages) for class
"model.frame".  Perhaps that is why R omitted the class.

However, S+ 8.3's (and problably S's) formula.data.frame did look for a
"terms" attribute of a data.frame before making up an additive formula
based on the column names of a data.frame:

Splus-8.3> formula.data.frame
function(object)
{
        if(length(tms <- attr(object, "terms")))
                return(formula(tms))
        n <- names(object)
        f <- paste(n[-1.], collapse = "+")
        f <- parse(text = paste(n[1.], f, sep = "~"))[[1.]]
        oldClass(f) <- "formula"
        f
}



Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Fri, Dec 21, 2018 at 8:16 AM Fox, John <jfox using mcmaster.ca> wrote:

> Dear Martin,
>
> Since no one else has picked up on this, I’ll take a crack at it:
>
> 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.
>
> 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 are eventually superseded by specific model.frame methods or do something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 <maechler using 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
> >
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>

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