Re: R-beta: formula() and model formulae
Thomas Lumley (thomas@biostat.washington.edu)
Tue, 6 May 1997 12:36:16 -0700 (PDT)
Date: Tue, 6 May 1997 12:36:16 -0700 (PDT)
From: Thomas Lumley <thomas@biostat.washington.edu>
To: r-testers <r-testers@stat.math.ethz.ch>
Subject: Re: R-beta: formula() and model formulae
In-Reply-To: <x2d8r4shh0.fsf@bush.kubism.ku.dk>
On 6 May 1997, Peter Dalgaard BSA wrote:
> Mike Meyer <mikem@stat.cmu.edu> writes:
> >
> > Several bugs (no solutions, yet). These might be well known.
> >
> > 1) If one does, e.g., mymod <- lm(y ~ x); formula(mymod)
> > then one does not get back the formula (one gets, Error: invalid formula)
>
> Yep. Seems that we need a
>
> formula.lm<-function(x)formula(x$terms)
>
We also need to fix formula.default. At the moment it only looks for
x$formula. Other standard places to keep a formula are x$call$formula and
x$terms. How about
formula.default<-function (x)
{
if (!is.null(x$formula))
return(eval(x$formula))
if (!is.null(x$call$formula))
return(eval(x$call$formula))
if (!is.null(x$terms))
return(x$terms)
switch(typeof(x), NULL = structure(NULL, class = "formula"),
character = formula(eval(parse(text = x)[[1]])),
call = eval(x), stop("invalid formula"))
}
One disdvantage to extracting the formula from $terms instead of
$call$formula is that in S a terms object is not a formula. On the other
hand it doesn't really matter as long as people use the formula()
function.
Thomas Lumley
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