[R] passing formula arguments cv.glm

[Adaikalavan Ramasamy]

I am trying to write a wrapper for the last example in help(cv.glm) that
deals with leave-one-out-cross-validation (LOOCV) for a logistic model.
This wrapper will be used as part of a bigger program. 

Here is my wrapper funtion :

   logistic.LOOCV.err <- function( formu=NULL, data=NULL ){

     cost.fn <- function(cl, pred) mean( abs(cl-pred) > 0.5 )

     glmfit <- glm( formula=formu, data=data, family="binomial" )
     print("glmfit is OK")
  
     err    <- cv.glm( data=data, glmfit=glmfit, 
                       cost=cost.fn, K=nrow(data) )$delta[2]
     print("cv.glm OK")
   }


When I run the above function line by line with the arguments from
below, it works fine. But when I call it as function, I get this :

   rm( glmfit, formu, cv.err ) # cleanup if required
   logistic.LOOCV.err( formu=as.formula(r~stage+xray+acid), data=nodal )

 logistic.LOOCV.err( formu=as.formula(r~stage+xray+acid), data=nodal )
[1] "glmfit is OK"
Error in model.frame(formula = formu, data = data[j.in, , drop =
FALSE],  : 
	Object "formu" not found


I think this has something to do with formula and environments but I do
not know enough to solve it myself. I searched the archive without much
help (perhaps I was using the wrong keywords).

Any help would be very much appreciated. Thank you.

Regards, 
-- 
Adaikalavan Ramasamy                    ramasamy at cancer.org.uk
Centre for Statistics in Medicine       http://www.ihs.ox.ac.uk/csm/
Wolfson College Annexe                  Tel : 01865 284 408
Linton Road, Oxford OX2 6UD             Fax : 01865 284 424