Feature Request: derive_vars_transposed to preserve expected variables

[yurovska]

Feature Idea

It would be nice if derive_vars_transposed could create the exact set of variables that are expected in the output even if some keys are missing in the data for the moment.

Relevant Input

No response

Relevant Output

No response

Reproducible Example/Pseudo Code

library(dplyr)
library(admiral)

# Example EX with Up-Titration scheme by Visit

ex <- admiral::ex_single %>%
  filter(
    USUBJID == "01-701-1097"
  ) %>%
  mutate(
    EXDOSE = case_when(
      VISIT == "BASELINE" ~ 2,
      VISIT == "WEEK 2" ~ 4,
      VISIT == "WEEK 24" ~ 8
    )
  )

# Example ADSL with the same subject

adsl <- admiral::admiral_adsl %>%
  filter(
    USUBJID == "01-701-1097"
  )

# Derive Study Day of First Dose for each dose level (TR2MGDY / TR4MGDY / TR8MGDY)

adsl_test1 <-  adsl %>%
  derive_vars_transposed(
    dataset_merge = 
      ex %>%
      group_by(USUBJID, EXDOSE) %>%
      slice_min(EXSTDY, n = 1) %>%
      mutate(
        TRXMGDY_KEY = paste0("TR", EXDOSE, "MGDY")
      ) %>%
      ungroup(),
    by_vars = exprs(USUBJID),
    key_var = TRXMGDY_KEY,
    value_var = EXSTDY,
    filter = TRXMGDY_KEY %in% c("TR2MGDY", "TR4MGDY", "TR8MGDY")
  )

# Perfect, all 3 variables are there in ADSL now

adsl_test1 %>%
  select(USUBJID, TR2MGDY, TR4MGDY, TR8MGDY)

# But let's say no subjects have reached 8 mg yet

ex_no_8mg <- ex %>%
  filter(
    EXDOSE != 8
  )

# Call `derive_vars_transposed` again

adsl_test2 <-  adsl %>%
  derive_vars_transposed(
    dataset_merge = 
      ex_no_8mg %>%
      group_by(USUBJID, EXDOSE) %>%
      slice_min(EXSTDY, n = 1) %>%
      mutate(
        TRXMGDY_KEY = paste0("TR", EXDOSE, "MGDY")
      ) %>%
      ungroup(),
    by_vars = exprs(USUBJID),
    key_var = TRXMGDY_KEY,
    value_var = EXSTDY,
    filter = TRXMGDY_KEY %in% c("TR2MGDY", "TR4MGDY", "TR8MGDY")
  )

# TR8MGDY is not there now
# and there is no way to preserve it within `derive_vars_transposed` call

adsl_test2 %>%
  select(USUBJID, TR2MGDY, TR4MGDY, TR8MGDY)