Weird behavior of*vlookup (SSC, user kcrow)

[Jorrit Gosens]

In short, when a value of edu is missing, it reports:

multiple observations with different edu within pid.

Whilst if values of edu are indeed not unique within pid, no error message is reported, where I would expect one.

This is version version 1.0.1 31oct2015, the most current version of vlookup, and on Stata 15.1.

Edit:
Tagging user Kevin Crow (StataCorp) here
Apologies, not from SSC, source is:

net install vlookup, from(http://www.stata.com/users/kcrow/)

* This runs fine
clear
input pid mother_id edu
 3115572 19556 40
 27313 19556 10
 19556 . 20
 end
vlookup mother_id, gen(mother_edu) key(pid) value(edu)

* where "value(edu)" is missing, a difficult to understand error message is reported about the uniqueness of edu within pid
* I would simply expect missing values to be assigned
clear
input pid mother_id edu
 3115572 19556 40
 27313 19556 10
 19556 . .
 end
vlookup mother_id, gen(mother_edu) key(pid) value(edu)

* where edu is not unique within pid, no error message is reported, vlookup simply assigns the last value of edu to mother_edu
clear
input pid mother_id edu
 3115572 19556 40
 27313 19556 10
 19556 . 20
 19556 . 10
 19556 . 8
 end
vlookup mother_id, gen(mother_edu) key(pid) value(edu)

[Robert Werth]

Jorrit Gosens not sure if you figured out a workaround. I encountered a similar bug recently and posted a separate question. William Lisowski very kindly offered a workaround for vlookup in reply to my question, which you (or others who find this later) may find useful: https://www.statalist.org/forums/for...ror-in-vlookup.