On Mon, 2007-07-16 at 14:57 +0100, [EMAIL PROTECTED] wrote: > On 16-Jul-07 13:28:50, Gabor Grothendieck wrote: > > The formula attribute of the builtin CO2 dataset seems a bit strange: > > > >> formula(CO2) > > Plant ~ Type + Treatment + conc + uptake > > > > What is one supposed to do with that? Certainly its not suitable > > for input to lm and none of the examples in ?CO2 use the above. > > I think one is supposed to ignore it! (Or maybe be inspired to > write a mail to the list ... ). > > I couldn't find anything that looked like the above formula from > str(CO2). But I did spot that the order of terms in the formula: > Plant, Type, treatment, conc, uptake, is the same as the order > of the "columns" in the dataframe.
CO2 is a groupedData object not a data.frame per se. > class(CO2) [1] "nfnGroupedData" "nfGroupedData" "groupedData" "data.frame" What Gabor saw was the result of formula.data.frame being applied to CO2, which, as you surmise Ted, is being produced from the columns of CO2. > formula(CO2) Plant ~ Type + Treatment + conc + uptake > stats:::formula.data.frame(CO2) Plant ~ Type + Treatment + conc + uptake But if we load nlme, we see that now (via a groupedData method for formula) a more useful formula is displayed. > require(nlme) Loading required package: nlme [1] TRUE > formula(CO2) uptake ~ conc | Plant as this can then be directly used in lme > lme(CO2) Linear mixed-effects model fit by REML Data: CO2 Log-restricted-likelihood: -283.1447 Fixed: uptake ~ conc (Intercept) conc 19.50028981 0.01773059 <snip /> But like Gabor, I'm struggling to see where this [formula(data.frame)] might be used (useful)? G -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Gavin Simpson [t] +44 (0)20 7679 0522 ECRC, UCL Geography, [f] +44 (0)20 7679 0565 Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ UK. WC1E 6BT. [w] http://www.freshwaters.org.uk %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
