get_risk_table: Convert simulated survival data set into risk table format.
In borealexander/tslrt: Function for treatment switching logrank test

get_risk_table Calculate risk table for a simulated two-arm survival data set.

1	get_risk_table(dt)

`dt`	Data frame containing simulated survival data set in standard format. Three columns: survival time `time`, whether patient has an `event` (1 = yes, 0 = censored), and treatment `group` (`control` or `experimental`).

A risk table with columns: t the event times, in ascending order n_e the number of patients at risk on the experimental treatment arm just prior to t. n_c the number of patients at risk on the control treatment arm just prior to t. d_e the number of events on the experimental arm at time t. d_c the number of events on the control arm at time t. n = n_e + n_c. d = d_e + d_c. l = l_e + l_c. l_e the number of patients on the experimental treatment arm who censored after the current t but before the subsequent t.