Identifying patient-IDs with two variables in common

[Cathrine Christiansen]

I have a dataset with many subjects (patient-IDs) with many observations per patient. I would like to find out how many patients that got medicine 1 (med1) each year. In the example dataset med1 is given three times in 2012, but only to two different patients.
I tried
bys PatientID (med1): gen med1pat=!mi(med1[1])
to first identify all patients that got med1 at any time.

Then
by PatientID: gen med1pat_2012=1 if med1==1 & year==2012
by PatientID: gen uniqu_med1pat_2012=1 if _n==1 & med1pat_2012==1
by PatientID: gen med1pat_2013=1 if med1==1 & year==2013
by PatientID: gen uniqu_med1pat_2013=1 if _n==1 & med1pat_2013==1

This gave me the right answer for 2012, med1 given three times (tab med1pat_2012: 3) and to two specific patients (tab unique_med1pat_2012: 2)
But for 2013 it got wrong...

* Example generated by -dataex-. For more info, type help dataex
clear
input byte PatientID int year byte med1 float(med1pat uniqu_med1pat med1pat_2012 uniqu_med1pat_2012 med1pat_2013 uniqu_med1pat_2013)
1 2012 1 1 1 1 1 . .
1 2014 1 1 . . . . .
1 2012 1 1 . 1 . . .
1 2013 . 1 . . . 1 .
1 2015 . 1 . . . . .
2 2013 1 1 1 . . 1 1
2 2014 1 1 . . . . .
2 2014 1 1 . . . . .
2 2015 . 1 . . . . .
2 2012 . 1 . 1 . . .
3 2012 . 0 . . . . .
3 2014 . 0 . . . . .
3 2015 . 0 . . . . .
3 2013 . 0 . . . . .
4 2012 1 1 1 1 1 . .
4 2013 1 1 . . . 1 .
4 2015 1 1 . . . . .
4 2015 1 1 . . . . .
4 2014 . 1 . . . . .
end

Thank you for helping.

[Carlo Lazzaro]

Cathrine:
do you mean something along the following lines?

. bysort PatientID year: egen wanted=sum( med1)

. list PatientID year med1 wanted

     +---------------------------------+
     | Patien~D   year   med1   wanted |
     |---------------------------------|
  1. |        1   2012      1        2 |
  2. |        1   2012      1        2 |
  3. |        1   2013      .        0 |
  4. |        1   2014      1        1 |
  5. |        1   2015      .        0 |
     |---------------------------------|
  6. |        2   2012      .        0 |
  7. |        2   2013      1        1 |
  8. |        2   2014      1        2 |
  9. |        2   2014      1        2 |
 10. |        2   2015      .        0 |
     |---------------------------------|
 11. |        3   2012      .        0 |
 12. |        3   2013      .        0 |
 13. |        3   2014      .        0 |
 14. |        3   2015      .        0 |
 15. |        4   2012      1        1 |
     |---------------------------------|
 16. |        4   2013      1        1 |
 17. |        4   2014      .        0 |
 18. |        4   2015      1        2 |
 19. |        4   2015      1        2 |
     +---------------------------------+

.

[Øyvind Snilsberg]

perhaps,

egen tag = tag(PatientID year) if med1==1
bys year: egen wanted = total(tag)