Compute AIC in Survival Analysis (survfit/coxph)

Question

I want to compute the AIC value for my survival analysis objects (suvfit/coxph). When I try to do it, it says:

> AIC(cox)
  Error in UseMethod("logLik") : 
   no applicable method for 'logLik' applied to an object of class "coxph"

For what I understand that's a software limitation. Can anyone help me to solve this problem without computing the AIC value by hand?

Answer 1

The function extractAIC has a method for coxph

fit <- coxph(Surv(time, status) ~ sex, data = cancer)
extractAIC(fit)

Answer 2

I remember I was computing it by hand, like this

p <- 0;k <- 3 
AIC0 <- -2*cox$loglik[1] + 2*(p+k)
p <- length(cox$coef)
AIC1 <- -2*cox$loglik[2] + 2*(p+k)