On Nov 16, 2009, at 2:31 PM, shuai yuan wrote:
Hi, there,
My appologize if someone ask the same question before. I searched the
mailing list and found one similar post, but not what i want.
The problem for me is, I use the step( glm()....) to do naive forward
selection for logistic regression. My code is functional
in the open environment. But if I wrap it up as a function, then R
keeps
saying "object 'a' not found". Actually, data frame
"a" is inside the function.
I did some search online. i guess the reason may be R did not keep
the data
in glm() output after building the model but not sure.
Can anyone please tell me how to work around this problem?
Thanks a lot in advance.
I am using R 2.9.0. Here is the sample code:
#------------
naivelr<-function(x,y){
:
:
:
a<-data.frame(x)
form<-
paste("y~1+",paste(grep("X.*",names(a),value=T),collapse="+"),sep="")
if(is.null(force.in)!=T){
lowmo<-paste("y~1+",paste(grep("X.*",names(a)
[force.in],value=T),collapse="+"),sep="")
} else
{lowmo<-"y~1"}
lower1<-glm(lowmo,family="binomial",data=data.frame(a,y))
upper1<-glm(form,family="binomial",data=data.frame(a,y))
You are sticking data.frame= a inside another data.frame ????
stepout<-
step
(lower1
,scope
=list(lower=lower1,upper=upper1),direction="forward",k=0,trace=100)
Thats not the way I remember "step"-ping. I thought you made a fit and
then "stepped" the formulas (using the same data), rather putting the
whole glm object into a "lower" and an "upper". I could be wrong about
that since I try to avoid using stepwise methods.
# here is the error:Start:
#AIC=689.62
#y ~ 1
#Error in data.frame(a, y) : object 'a' not found---but "a" is there!
But it's probably not in a form that can be interpreted. Consider
adding y as a column in "a".
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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