### survival function for the lifetimes of guinea pigs - Example A p.349

# c1 lifetime c2 status c3 group

gpig <- matrix(scan("H:\\hw3\\gpig1.dat"),ncol=3,byrow=T)

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

dimnames(gpig) 

gpig.data <- data.frame(gpig)

gpig.data

gpig.data$time
gpig.data$status
gpig.data$group

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

# plot the survival functions for the groups on the same plot, Kaplan-Meier

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

plot(fit, lty = 0:5, xlab="Days elapsed",ylab="Proportion of live animals")

summary(fit)

# comparing Kaplan-Meier Survival Curves

survdiff(Surv(time, status) ~ group, data = gpig.data)

# Fit an exponential model

fit.exp <- survReg(Surv(time, status) ~ group, data = gpig.data, dist="exponential")

summary(fit.exp)