Description

When functions add_n() and add_p() are run after tbl_survfit(), the original call to survival::survfit() is extracted and the formula= and data= arguments are used to calculate the N or p-value.

When the values of the formula= and data= are unavailable, the functions cannot execute. Below are some tips to modify your code to ensure all functions run without issue.

1. Let tbl_survfit() construct the survival::survfit() for you by passing a data frame to tbl_survfit(). The survfit model will be constructed in a manner ensuring the formula and data are available. This only works if you have a stratified model.

   Instead of the following line

   survfit(Surv(ttdeath, death) ~ trt, trial) %>%
     tbl_survfit(times = c(12, 24))
   

   Use this code

   trial %>%
     select(ttdeath, death, trt) %>%
     tbl_survfit(y = Surv(ttdeath, death), times = c(12, 24))
   

2. Construct an expression of the survival::survfit() before evaluating it. Ensure the formula and data are available in the call by using the tidyverse bang-bang operator, !!.

   Use this code

   formula_arg <- Surv(ttdeath, death) ~ 1
   data_arg <- trial
   rlang::expr(survfit(!!formula_arg, !!data_arg)) %>%
     eval() %>%
     tbl_survfit(times = c(12, 24))