Hi all

I am having a hard time thinking about the best way to balance this dataset. The format is:
plan ID State Year Drug
1a AL 2012 Abilify
1a AL 2012 Humalog
2a AL 2012 Abilify
2a AL 2012 Novolog
1a AL 2013 Abilify
1a AL 2013 Humalog
1a AL 2013 Humira
I need each plan/state/year to have an observation for every drug that is listed on any plan in that year. In my example table, Plan 1a in AL in 2012 would need to also have a row for Novolog, because Plan 2a has Novolog in 2012. Plan 2a in AL in 2012 would conversely need a row for Humalog, because Plan 1a has it in that year.

Any advice for how I could code this? Much appreciated, thank you!