On Wed, 26 May 2004, Berwin A Turlach wrote:
> Dear Brian,
>
> >>>>> "BDR" == Prof Brian Ripley <[EMAIL PROTECTED]> writes:
>
> BDR> The problem is not in update but in glm itself: take a look
> BDR> at fm$formula after the first fit. fm$terms has the right
> BDR> formula, but formula() extracts the $formula component first.
> O.k., I see what you mean.
>
> BDR> I am not currently sure what the right fix is, so will not
> BDR> try to fix this in R-patched/1.9.1.
> This may be naive, but I noticed the following at the end of the glm
> function (starting line 76, in src/library/stats/R/glm.R):
>
> fit <- c(fit, list(call = call, formula = formula,
> terms = mt, data = data,
> offset = offset, control = control, method = method,
> contrasts = attr(X, "contrasts"),
> xlevels = .getXlevels(mt, mf)))
>
> That is, the component "formula" in the object that is returned is
> explicitly set to the "formula" argument with which glm was called.
> The function "lm" does not do this. And if I change this `line' to
>
> fit <- c(fit, list(call = call,
> terms = mt, data = data,
> offset = offset, control = control, method = method,
> contrasts = attr(X, "contrasts"),
> xlevels = .getXlevels(mt, mf)))
>
> then fm$formula for the first fit in my example looks o.k.
You won't have a formula component at all (lm objects do not).
What I have done is alter the formula methods to pick up the formula from
the terms component but the environment from the formula componet (if
present).
>
> But I don't know if this will break anything else.
>
> Cheers,
>
> Berwin
>
> PS: I noticed that both `glm' and 'lm' now do essentially the
> following manipulations early on:
>
> mf <- match.call(expand.dots = FALSE)
> m <- match(c("formula", "data", "subset", "weights", "na.action",
> "offset"), names(mf), 0)
> mf <- mf[c(1, m)]
> mf$drop.unused.levels <- TRUE
> mf[[1]] <- as.name("model.frame")
> mf <- eval(mf, parent.frame())
>
> Is this the preferred idiom to be used in R 1.9.x and later for
> modelling functions?
Rather than removing components, by setting to NULL, yes.
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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