[R] Arbitrary number of covariates in a formula

[Erik Iverson]

Are you for some reason against writing your function to accept a single 
argument, a formula, that you simply pass on to coxph?

Mendolia, Franco wrote:
> Hello!
> 
> I have something like this:
> 
> test1 <- data.frame(intx=c(4,3,1,1,2,2,3), 
>                    status=c(1,1,1,0,1,1,0), 
>                    x1=c(0,2,1,1,1,0,0), 
>                    x2=c(1,1,0,0,2,2,0), 
>                    sex=c(0,0,0,0,1,1,1)) 
>                    
> and I can easily fit a cox model:
> 
> library(survival)
> coxph(Surv(intx,status) ~ x1 + x2 + strata(sex),test1)
> 
> However, I want to write my own function, fit the model inside this function and then do some further computations.
> 
> f <- function(time, event, stratum, covar )
> {
> 
>   fit <- coxph(Surv(time,event) ~ covar[[1]] + covar[[2]] + strata(stratum))
>   fit
>   #... do some other stuff
> }
> 
> attach(test1)
> f(intx, status, sex, list(x1,x2))
> 
> This works fine when I have exactly two covariates. However, I would like to have something that I can use with an arbitrary number of covariates. More precisely, I need something more general than covar[[1]] + covar[[2]].
> 
> Any ideas?
> 
> Thanks,
> Franco
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