[R] formula error inside function

[moli]

I want use survfit() and basehaz() inside a function, but it doesn't work.
Could you take a look at this problem. Thanks for your help. Following is my
codes: 

library(survival)
n <- 50      # total sample size
nclust <- 5  # number of clusters
clusters <- rep(1:nclust,each=n/nclust)
beta0 <- c(1,2)
set.seed(13)
#generate phmm data set
Z <- cbind(Z1=sample(0:1,n,replace=TRUE),
       Z2=sample(0:1,n,replace=TRUE),
       Z3=sample(0:1,n,replace=TRUE))
b <-
cbind(rep(rnorm(nclust),each=n/nclust),rep(rnorm(nclust),each=n/nclust))
Wb <- matrix(0,n,2)
for( j in 1:2) Wb[,j] <- Z[,j]*b[,j]
Wb <- apply(Wb,1,sum)
T <- -log(runif(n,0,1))*exp(-Z[,c('Z1','Z2')]%*%beta0-Wb)
C <- runif(n,0,1)
time <- ifelse(T<C,T,C)
event <- ifelse(T<=C,1,0)
mean(event)
phmmd <- data.frame(Z)
phmmd$cluster <- clusters
phmmd$time <- time
phmmd$event <- event

fmla <- as.formula("Surv(time, event) ~ Z1 + Z2")

BaseFun <- function(x){
start.coxph <- coxph(x, phmmd)  

print(start.coxph)

betahat <- start.coxph$coefficient
print(betahat) 
print(333)  
print(survfit(start.coxph))                                                                                                                                                                                                                                     
m <- basehaz(start.coxph)
print(m)
}  
BaseFun(fmla)



Error in formula.default(object, env = baseenv()) : invalid formula


But the following function works:
coxph(fmla, phmmd)

--
View this message in context: http://r.789695.n4.nabble.com/formula-error-inside-function-tp4326549p4326549.html
Sent from the R help mailing list archive at Nabble.com.