Set up a count variable with a filter

[Filipp Sabitzer]

Hi all, i would like to add a new variable with a counter. For the following dataset I would like to add a 4th variable which will be the mentioned counter. The counter should count the number of B observations for a given A observation when the filter equals 1. For example: the first count value should be 2 because the observation "1" in B occurs twice for the observation "1" in A given that the filter equals 1. * Example generated by -dataex-. To install: ssc install dataex clear input int(A B filter) 1 1 1 1 2 0 1 3 0 1 2 0 1 3 1 1 1 1 1 4 0 2 4 0 2 2 1 2 3 1 2 3 0 3 1 0 3 2 0 end I would appreciate any kind of help. Thank you very much.

[Filipp Sabitzer]

Sorry for the visualisation. I hope this time it works. Code: * Example generated by -dataex-. To install: ssc install dataex clear input int(A B wanted) 1 1 1 1 2 0 1 3 0 1 2 0 1 3 1 1 1 1 2 4 0 2 2 1 2 3 1 2 3 0 3 1 0 3 2 0 end

[Filipp Sabitzer]

A B filter
1 1 1
1 2 0
1 3 0
1 2 0
1 3 1
1 1 1
2 4 0
2 2 1
2 3 1
2 3 0
3 1 0
3 2 0

[William Lisowski]

Here is code using your example data that seems to do what you want.

. clear

. input int(A B filter)

            A         B    filter
  1. 1 1 1
  2. 1 2 0
  3. 1 3 0
  4. 1 2 0
  5. 1 3 1
  6. 1 1 1
  7. 2 4 0
  8. 2 2 1
  9. 2 3 1
 10. 2 3 0
 11. 3 1 0
 12. 3 2 0
 13. end

. bysort A B : egen count = total(filter==1)

. list, noobs sepby(A B)

  +------------------------+
  | A   B   filter   count |
  |------------------------|
  | 1   1        1       2 |
  | 1   1        1       2 |
  |------------------------|
  | 1   2        0       0 |
  | 1   2        0       0 |
  |------------------------|
  | 1   3        1       1 |
  | 1   3        0       1 |
  |------------------------|
  | 2   2        1       1 |
  |------------------------|
  | 2   3        0       1 |
  | 2   3        1       1 |
  |------------------------|
  | 2   4        0       0 |
  |------------------------|
  | 3   1        0       0 |
  |------------------------|
  | 3   2        0       0 |
  +------------------------+