It is not terribly important, but I had a model.frame which I forgot was a model.frame and was surprised that lm(modelFrame) gave me a result based on the different formula than formula(modelFrame) showed.
S+'s formula() makes those consistent (and it also makes model.frame's output have class "model.frame" instead of just "data.frame"). That is inherited from S version 3. R has formula methods (especially in package:nlme) to extract the formula from lots of other kinds of objects, but not for model.frames. Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -----Original Message----- > From: Prof Brian Ripley [mailto:rip...@stats.ox.ac.uk] > Sent: Wednesday, January 19, 2011 6:50 AM > To: William Dunlap > Cc: r-devel@r-project.org > Subject: Re: [Rd] formula(model.frame(y~.^2, data=d)) does > not return formula from terms attribute of the model.frame > > On Thu, 6 Jan 2011, William Dunlap wrote: > > > In R 2.12.0 I get > > > d <- data.frame(x=1:10, y=log(1:10), > f3=LETTERS[rep(1:3,c(3,3,4))]) > > > m <- model.frame(y~.^2, data=d) > > > formula(m) > > y ~ x + f3 > > In S+ formula(m) gives formula given to model.frame(), > > but in R you have to do the following get that formula: > > > formula(attr(m, "terms")) > > y ~ (x + f3)^2 > > But that has the advantage that you almost certainly have a model > frame and hence that is what you intend. With 6-6 (or 20-20 in > Imperial units) hindsight it would have been better to give model > frames a class inheriting from "data frame", but it seems that the > presence of attr(, "terms") is the most common test. > > > Would it break anything to add to the top of > > Unfortunately, that is rather hard to tell! > > > formula.data.frame > > something like > > if (!is.null(tms <- attr(x, "terms"))) { > > return(formula(tms)) > > } > > so that formula() would retrieve the formula buried > > in model.frame's output? > > I looked (not hard, but without success) for examples of calling > formula() on a data frame. I did see that > model.frame.default() calls > as.formula() on a data frame, but only after checking for the absence > of a "terms" attribute. > > Can you explain where it would help? I think we need to see examples > to see if a change in meaning would be clearly beneficial. I can > envisage cases in which 'x' was a data frame that just happened to > have been constructed as a model frame and where the currently > documented meaning was intended. > > > Bill Dunlap > > Spotfire, TIBCO Software > > wdunlap tibco.com > > -- > Brian D. Ripley, rip...@stats.ox.ac.uk > 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 > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
