Question

I want to assign the same id number to every four observations. For example, if I have the following data

age marital gender  id
45  1   0   1
33  1   1   1
68  0   1   1
27  1   0   1
43  0   0   2
37  0   1   2
19  1   1   2
40  1   1   2
25  1   0   3
38  1   1   3
57  0   0   3
50  1   0   3
51  1   1   4
44  0   1   4
69  1   0   4
39  0   1   4

The last column id is something I want to produce.
Plus, the dataset have 500,000+ observations.

Thanks in advance.

Answer 1

Use the integer function and the built-in _n_ variable (which increments for each observation):

id = int( (_n_-4)/4 )+1;