Re: [Rd] Guidelines for writing model term functions (?)

From: Prof Brian Ripley <>
Date: Sat 03 Jul 2004 - 01:15:45 EST

Well, there are examples like log, too, and poly() is a good one.

poly, ns and bs are special because they participate in the safe prediction scheme (?SafePrediction). If you don't need that, just return a vector or matrix (whose columns will be treated as a set of vectors).

On Fri, 2 Jul 2004, Roger D. Peng wrote:

> Are there any general guidelines for writing functions that appear in
> model formulas for functions like lm()/glm()? The ones I can think of
> are ns()/bs() in `splines' and s() in `mgcv'. It seems that ns()/bs()
> basically create matrix with a number of attributes and a class, while
> s() returns a list of parameters. It seems that gam() in `mgcv' has
> its own way of dealing with formulas so maybe that's not a great
> example, but are there any suggestions for writing a function that
> might appear in the formula for, say, lm() or glm()?

Brian D. Ripley,        
Professor of Applied Statistics,
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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