R version 4.4.0 RC (2024-04-16 r86458 ucrt) -- "Puppy Cup"
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> library(survival)
> #
> # A test of nesting.  It makes sure the model.frame is built correctly
> #
> tfun <- function(fit, mydata) {
+     survfit(fit, newdata=mydata)
+     }
> 
> myfit <- coxph(Surv(time, status) ~ age + factor(sex), lung)
> 
> temp1 <- tfun(myfit, lung[1:5,])
> temp2 <- survfit(myfit, lung[1:5,])
> indx <- match('call', names(temp1))  #the call components won't match
> 
> all.equal(unclass(temp1)[-indx], unclass(temp2)[-indx])
[1] TRUE
> 
> 
> proc.time()
   user  system elapsed 
   0.82    0.04    0.86