R-beta: formula() and model formulae

[Peter Dalgaard BSA]

Mike Meyer <mikem at stat.cmu.edu> writes:

> 
> Several bugs (no solutions, yet).  These might be well known.
> 
> 1) If one does, e.g.,  mymod <- lm(y ~ x); formula(mymod)
> then one does not get back the formula (one gets, Error: invalid formula) 

Yep. Seems that we need a

formula.lm<-function(x)formula(x$terms)

> 
> 2) if x is of mode numeric, then the model formula
> 	mymod <- lm(y ~ x + x^2)
> is not processed as S would do it. The model is fit ignoring the x^2 term, 

We had that topic a while back. I think it was concluded that it is a
feature, because mixing model formulas and arithmetic ditto is bad
practice. (I don't have any strong feeling about this, personally. As
long as R won't introduce those awful Helmert contrasts as default...)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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