Re: R-beta: formula() and model formulae
Gregory R. Warnes (warnes@biostat.washington.edu)
Wed, 7 May 1997 15:41:46 -0700 (PDT)
Date: Wed, 7 May 1997 15:41:46 -0700 (PDT)
From: "Gregory R. Warnes" <warnes@biostat.washington.edu>
To: Bill Venables <wvenable@attunga.stats.adelaide.edu.au>
Subject: Re: R-beta: formula() and model formulae
In-Reply-To: <9705070854.AA21728@attunga.stats.adelaide.edu.au>
On Wed, 7 May 1997, Bill Venables wrote:
> A term such as (a + b + x + y)^2 should be expanded out binomial
> fashion, coefficients stripped away and the remaining products
> treated as : products. Then S copes with terms like a:a, a:b and
> a:x fine, even x:y is handled by having it generate a column of
> xy-products, as it should.
>
> But a term such as x:x does not generate a column of x-squares,
> it is merely removed as it would be if it were a factor. This is
> a complete anomaly, and one that I don't think would be hard or
> dangerous for R to rectify. Indeed it would be very useful to
> generate a complete second degree regression in three variables
> using y ~ (1 + x1 + x2 + x3)^2.
Amen. Let it be!
> > (I don't have any strong feeling about this, personally. As
> > long as R won't introduce those awful Helmert contrasts as
> > default...)
ditto!
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Gregory R. Warnes | It is high time that the ideal of success
warnes@biostat.washington.edu | be replaced by the ideal of service.
| Albert Einstein
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