[R] test for a formulae

[Thomas Lumley]

On Fri, 2 Jun 2000, Prof Brian D Ripley wrote:

> On Fri, 2 Jun 2000, Paulo J. Ribeiro Jr wrote:
> 
> > I'd like to check within a whether an argument is a formulae of the type
> > ~X or similar.
> > What's the right way to do so?
> > 
> > I'm using: is.language(obj) but not sure this is right
> 
> That allows lots of other things.
> 
> Formulae have class "formula", so inherits(obj, "formula") looks best.
> 

And if you want to ensure that it is ~X+Z+W rather than Y~X+Z+W you can
use
 inherits(obj,"formula") && (length(obj)==2)


	-thomas

Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._