[R] survfit & number of variables != number of variable names

[Georges Dupret]

Hi!

In answer to:

--------
I noticed that you were using what might be called an "externally  
created Surv object". I have a memory that Terry Therneau has  
criticized that practice. I cannot remember if it was in exactly this  
situation but I might ask if setting up the model as:

cox = coxph(Surv(stime, event) ~ bucket*(today + accor + both) +  
activity, data = data)

... might give the survival machinery a better handle on where  
everything might be found. 
------------

I tried to create the Surv object "internally" but I face the same issue:

> (cox.s = coxph(Surv(time=absence, event=(censored==FALSE)) ~ 
> bucket*(today) + strata(activity), data = small))
Call:
coxph(formula = Surv(time = absence, event = (censored == FALSE)) ~ 
    bucket * (today) + strata(activity), data = small)

                       coef exp(coef) se(coef)      z    p
bucket575            0.4526     1.572    0.740  0.612 0.54
todayTRUE           -0.0886     0.915    0.676 -0.131 0.90
bucket575:todayTRUE -0.1670     0.846    0.794 -0.210 0.83

Likelihood ratio test=2.32  on 3 df, p=0.509  n= 100, number of events= 100 
> fit = survfit(cox.s, newdata=small[1:50,])
Error in model.frame.default(data = small[1:50, ], formula = ~bucket +  : 
  number of variables != number of variable names

Best, and thank you for the suggestion.

ge



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