[R] Error in calling stepAIC() from within a function

[Prof Brian Ripley]

Your example works for me in R-devel, and in R 1.7.1 using step()
rather than stepAIC().

On Sun, 3 Aug 2003, Siew Leng TENG wrote:

> Hi,
>  
>  I am experiencing a baffling behaviour of stepAIC(),
>  and I hope to get any advice/help on what went wrong
> or I'd missed. I greatly appreciate any advice given.
>  
>  I am using stepAIC() to, say, select a model via
>  stepwise selection method.
>  
>  R Version : 1.7.1
>  Windows ME
>  
>  Many thanks and best regards,
> Siew-Leng
>  
>  
>  ***Issue :
>  
>  When stepAIC() is placed within a function, it seems
>  that stepAIC() cannot detect the data matrix, and
>  the
>  program is halted as a result. However, when the
>  same
>  codes are copied, paste and run in R workspace,
>  stepAIC can execute and R is able to produce the
>  desired output.
>  
>  ***Actions taken :
>  I had tried to look into and manipulate environments
>  and formals(f), but with not much luck.
>  
>  
>  ***Code snippets (an example):
>  
>    library(MASS)
>    library(nls)
>  
>    Data<-data.frame(matrix(rnorm(120),ncol=6))
>    colnames(Data)<-c("Y",paste("X",1:5,sep=""))
>  
>    f<-function(A)
>    {
>    a <-glm(Y~X1+X2+X3, data=A)
>    b
> 
> <-stepAIC(a,scope=list(upper=~X1+X2+X3+X4+X5,lower=~1),direction="both",trace=FALSE)
>    b
>    }
>  
> 
>   f(Data) 
>  
>  
>  R gives the following error :
>  
>  > f(Data)
>  Error in model.frame.default(formula = Y ~ X1 + X3,
>  data = A, drop.unused.levels = TRUE) : 
>          Object "A" not found
>  
>  
>  However, when the same codes are copied, paste and
>  run
>  in the workspace, stepAIC() can run, and R is able
>  to
>  produce the desired output :
>  
>  A <- Data
>  a <-glm(Y~X1+X2+X3, data=A)
>  b
> 
> <-stepAIC(a,scope=list(upper=~X1+X2+X3+X4+X5,lower=~1),direction="both",trace=FALSE)
>  b
>  
> > b
>  
> > Call:  glm(formula = Y ~ X4, data = A) 
> > 
> > Coefficients:
> > (Intercept)           X4  
> >      0.1942      -0.3314  
> > 
> > Degrees of Freedom: 19 Total (i.e. Null);  18
> > Residual
> > Null Deviance:      20.51 
> > Residual Deviance: 17.95        AIC: 60.6 
> > > 
> 
> 
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-- 
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