### survival function for the survival times of hepetitis patients

hepa <- matrix(scan("H:\\hw3\\hepatitis.dat"),ncol=3,byrow=T)

dimnames(hepa) <- list(NULL, c("time","status","group"))		# dimnames fills names row by cols

dimnames(hepa) 

hepa.data <- data.frame(hepa)

hepa.data

hepa.data$time
hepa.data$status
hepa.data$group

Surv(hepa.data$time, hepa.data$status)

# plot the survival functions for the hepatitis data, Kaplan-Meier

fit <- survfit(Surv(time, status) ~ group, data = hepa.data)

plot(fit, xlab="Weeks elapsed",ylab="Proportion of live patients")

# Fit an exponential model

survReg(Surv(time, status) ~ group, data = hepa.data, dist="exponential")