Hi, I am trying to generate the index "z" in Stata, so that Z has the same value for all Xs and Ys. For example:

x y z
1 1 1
1 2 1
1 3 1
2 4 2
2 5 3
2 6 3
4 7 4
5 2 1
6 3 1
7 8 5

Any help would be much appreciated. Thanks!