Sorry, I still cannot find what's wrong with it. And it seems that
nothing is wrong with t.
Jia
> z1<-rnorm(N,0,1)
> z2<-rnorm(N,3,5)
> z3<-rbinom(N,1,0.6)
>
> prop.cens<-0.45
> cen<-rbinom(N,1,1-prop.cens) #<-- censor indicator:45% censor in
the data.
> t<- rexp(N)
> all<-data.frame(z1,z2,z3)
> fit.model.all<- coxph(Surv(t,cen) ~z1+z2+z3,data=all)
> fit.model.all
Call:
coxph(formula = Surv(t, cen) ~ z1 + z2 + z3, data = all)
coef exp(coef) se(coef) z p
z1 0.057466 1.059 0.1377 0.4173 0.68
z2 0.000907 1.001 0.0332 0.0273 0.98
z3 -0.349273 0.705 0.2867 -1.2184 0.22
Likelihood ratio test=1.81 on 3 df, p=0.613 n= 100
> reg.model.all<-step(fit.model.all)
Start: AIC= 376.39
Surv(t, cen) ~ z1 + z2 + z3
Error in as.data.frame.default(data) : cannot coerce class "function"
into a data.frame
_____
From: Hong Ooi [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 15, 2006 10:53 AM
To: Li, Jia
Subject: RE: [R] A question about stepwise procedures: step function
Note: This e-mail is subject to the disclaimer contained at the bottom
of this message.
_____
t is the name of a function. If you have a variable called t in your
dataset, try renaming it.
_____
From: [EMAIL PROTECTED] on behalf of Li, Jia
Sent: Thu 15/06/2006 11:52 PM
To: [email protected]; [EMAIL PROTECTED]
Subject: Re: [R] A question about stepwise procedures: step function
Hi,
Step works for a Cox model. And I got the same error massage using
stepAIC.
Jia
_____
From: Ritwik Sinha [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 15, 2006 12:12 AM
To: Li, Jia
Subject: Re: [R] A question about stepwise procedures: step function
Hi,
The step documentation says
"object: an object representing a model of an appropriate class
(mainly '"lm"' and '"glm"'). This is used as the initial
model in the stepwise search.
"
I wonder if it will work for a cox proportional hazard model. You could
try stepAIC in MASS.
On 6/14/06, Li, Jia < [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> >
wrote:
Dear all,
I tried to use "step" function to do model selection, but I got
an error massage. What I don't understand is that data as data.frame
worked well for my other programs, how come I cannot make it run this
time. Could you please tell me how I can fix it?
************************************************************************
***************************
>all<-data.frame(z1,z2,z3)
>fit.model.all<- coxph(Surv(t,cen) ~z1+z2+z3,data=all)
> reg.model.all<-step(fit.model.all)
Start: AIC= 689.1
Surv(t, cen) ~ z1 + z2 + z3
Error in as.data.frame.default(data) : cannot coerce class
"function" into a data.frame
************************************************************************
***************************
Thanks a lot!
Jia
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--
Ritwik Sinha
Graduate Student
Epidemiology and Biostatistics
Case Western Reserve University
http://darwin.cwru.edu/~rsinha
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