On Tue, 16 Aug 2005, Sundar Dorai-Raj wrote: > Uwe Ligges wrote: >> Laurent Valdes wrote: >> >> >>> I have seen, several times, dots (like this: "y ~." ) in formula >>> descriptions, noticeably in R help. >>> >>> I am unable to see what it does correspond to. >>> >>> Any ideas ? >> >> All other variables (except y) from the given data.frame... >> >> Uwe Ligges >> > > Hi, Uwe, > > Doesn't this depend on the context? For example, > > z <- data.frame(y = rnorm(10), x = rnorm(10)) > fit <- lm(y ~ ., z) > update(fit, y ~ . + I(x^2)) > > The original poster did not say where he saw this formula. However, I > think the reference in ?formula has the most authorative explanation.
(It does not cover this, as it is part of the interpretation of a formula.) Yes, it must depend on context, as an R function can do anything it likes with a formula (including making y ~ x mean the regression of x on y). If terms.formula() is used, y ~ . means what Uwe said, _if_ there is a 'data' argument. However, if not it has its literal meaning (a variable named '.'), at least until 2.2.0. -- 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 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html