Derive AVALC, AVAL and AVALU

[thomas-neitmann]

Close #62

[bundfussr]

At first glance the derive_aval function looks fine. But at second glance I wonder if it is really helpful.

• The name suggests that it is a general function for deriving aval. But I think it can be used for advs and adeg only. Maybe also for some parameters in adlb and questionnaires datasets.
• The function derives the avalu variable which is Roche specific. CDISC ADaMIG suggests that the unit should be stored in param:

  Note that there is no separate units variable for BDS variables PARAM or AVAL, since the units of AVAL will be included in the value of PARAM.

• To support review and avoid black boxes you would need to add a comment before the derive_aval call like

  # derive AVAL, AVALC, and AVALU as VSSTRESN, VSSTRESC, and VSSTRESU respectively

So maybe it is better not implementing a function but just using mutate(AVAL = VSSTRESN, AVALC = VSSTRESC, AVALU = VSSTRESU).

What do you think?

[thomas-neitmann]

@aehmann-gsk I'd be interested to hear your thoughts on this.

[aehmann-gsk]

@thomas-neitmann @bundfussr
I am ok with AVALU, we do have that defined in TA specific specs so it could be useful. I do have a concern the function will abort if all 3 (--stresc, --stresn, and --stresu are not present. This could limit the use of the function significantly because for questionnaires or anything that is not continuous, the --stresn and/or --stresu may not be present.

It may be more useful to have the function call be:
derive_aval <- function(dataset, AVALC = STRESC, AVAL = STRESN, AVALU = STRESU) {
and also allow for these items to be missing if they are not applicable. One last note, may want to think about situations where the AVAL/AVALC may not come from a findings domain - perhaps that is more ADaM specific and does not need to be addressed with this function, just something to think about.

[thomas-neitmann]

After giving it some more thought I agree with @bundfussr and would suggest that user would simply use mutate() to do the applicable mapping "manually".