R devel - Mar 2008 - how to exclude terms preceded by - from model frame

[I believe few users manipulate formulae and model frames like this, so
I'm posting here instead of R-help.]

I just found out that model.frame() includes all terms, including those
preceded by "-" in the formula, in its output (as mentioned on its
help
page).  Is there a recommended way of excluding "negative" terms?  My
guess is that I can use info in the terms attribute to figure this out,
but that doesn't seem very straightforward.  Any pointer would be much
appreciated.

Best,
Andy

Andy Liaw, PhD
Biometrics Research    PO Box 2000 RY33-300
Merck Research Labs        Rahway, NJ 07065
andy_liaw(a)merck.com          732-594-0820



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On Wed, 19 Mar 2008, Liaw, Andy wrote:
> [I believe few users manipulate formulae and model frames like this, so
> I'm posting here instead of R-help.]
>
> I just found out that model.frame() includes all terms, including those
> preceded by "-" in the formula, in its output (as mentioned on
its help
> page).  Is there a recommended way of excluding "negative" terms?
My
> guess is that I can use info in the terms attribute to figure this out,
> but that doesn't seem very straightforward.  Any pointer would be much
> appreciated.
?terms.formula, argument 'simplify', if I understand you aright.

>
> Best,
> Andy
>
> Andy Liaw, PhD
> Biometrics Research    PO Box 2000 RY33-300
> Merck Research Labs        Rahway, NJ 07065
> andy_liaw(a)merck.com          732-594-0820

-- 
Brian D. Ripley,                  ripley at 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