Given a data set in standard format (with one row per subject/observation),
this function adds a column with the specified exposure time points
and a column with respective exposures, created from `rng_fun`

.
This function should usually only be used to create data sets passed
to `sim_pexp`

.

`add_tdc(data, tz, rng_fun, ...)`

- data
A data set with variables specified in

`formula`

.- tz
A numeric vector of exposure times (relative to the beginning of the follow-up time

`t`

)- rng_fun
A random number generating function that creates the time-dependent covariates at time points

`tz`

. First argument of the function should be`n`

, the number of random numbers to generate. Within`add_tdc`

,`n`

will be set to`length(tz)`

.- ...
Currently not used.