Hi everyone,

So, I have a very large yearly database on students of different educational levels (3 Million observations per month).

What I need to do is to append all months together in order to form a balanced panel. In Month 1 (t=1), I have a database that looks like:

Id Year Educational Level
100 1 1
101 1 1
102 1 1
103 1 2
104 1 2
100 2 2
101 2 2
102 2 2
103 2 3

So what I want to do is to use an append command that only appends the subset of id's that had an educational level equal to 1 in the baseline years. So In the example above, I want to append people with Id 100 through 102, but not 103 through 104.

This is because the database is very large, so I need to do the append with only the essential observations, instead of merging everything and then dropping the observations I don't need.

Any help with this?

Regards,
Alejandro