R help - Feb 2012 - stepAIC error

i am trying to run stepwise regression for two models(lower,upper),
family=gamma
and i get the same error despite the models i use.

Error in UseMethod("extractAIC") : 
  no applicable method for 'extractAIC' applied to an object of class
"formula"
In addition: Warning message:
In nobs.default(object, use.fallback = TRUE) :
  no 'nobs' method is available

Any help?
Thanks

--
View this message in context:
http://r.789695.n4.nabble.com/stepAIC-error-tp4407460p4407460.html
Sent from the R help mailing list archive at Nabble.com.

labbig <lkaimaka <at> windowslive.com> writes:
> 
> i am trying to run stepwise regression for two models(lower,upper),
> family=gamma
> and i get the same error despite the models i use.
> 
> Error in UseMethod("extractAIC") : 
>   no applicable method for 'extractAIC' applied to an object of
class
> "formula"
> In addition: Warning message:
> In nobs.default(object, use.fallback = TRUE) :
>   no 'nobs' method is available
> 
  A reproducible example would definitely help.

  The "no 'nobs' method is available" warning is a clue that
you
may be using an older version of R (I believe 'nobs' was introduced
in version 2.13).
 
  If you possibly can, update to the latest version of R and
post a reproducible example.

  Ben Bolker