[R] test for a formulae

Prof Brian D Ripley ripley at stats.ox.ac.uk
Fri Jun 2 17:08:13 CEST 2000

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.

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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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