help with -expand-

[Yun Cheng]

Dear statalist,

I have a set of data which spans from 2019 to 2020, for some firms, the data only has 2019 or 2020, but not both years, for those cases, I want to manually create the missing year. I believe -expand- can do so, but I don't know how exactly.

Some data here

* Example generated by -dataex-. To install: ssc install dataex
clear
input long firm float year
  1 2020
  2 2019
  2 2020
  4 2020
  9 2019
  9 2020
 11 2019
 12 2019
 16 2020
 17 2020
 20 2020
 21 2020
 25 2020
 26 2019
 27 2019
 27 2020
 28 2019
 28 2020
 29 2019
 31 2019
 34 2019
 34 2020
 35 2019
 35 2020
 36 2019
 36 2020
 39 2019
 39 2020
 40 2019
 42 2020
 45 2020
 49 2020
 50 2019
 50 2020

For example, for firm 1, it only has 2020 but not 2019, so I want to create year 2019 for this firm; similarly, for firm 4, I want to create year 2019. Any help will be greatly appreciated.

[Joseph Coveney]

I think that you're probably more interested in fillin than expand.

Take a look at its helpfile

help fillin

and see whether that gets you where you want to go.

[Yun Cheng]

thanks it works well!