From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>

Date: Wed 17 Aug 2005 - 03:48:27 EST

Date: Wed 17 Aug 2005 - 03:48:27 EST

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, ripley@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-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.htmlReceived on Wed Aug 17 03:54:07 2005

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