. clear all
. input x y
1 1
1 1
1 2
2 1
2 2
1 1
2 1
2 1
1 2
2 2
end

. duplicates drop x y, force
. list

     +-------+
     | x   y |
     |-------|
  1. | 1   1 |
  2. | 1   2 |
  3. | 2   1 |
  4. | 2   2 |
     +-------+