First occurrence for every categorical variable

[Frank van Laan]

Dear Stata Users,

I have the following problem. I've panel data and I would like to create a dummy which indicates whether for that specific individual, the categorie occurred for the first time or not.

So, my data looks like this:

ID Time Category
1  1    A
1  1    B
1  1    C
1  1    D
1  2    B
1  2    D
1  2    E
1  3    A
1  3    B
1  3    E
2  1    B
2  1    D
2  1    E
2  2    B
2  2    E
2  3    A
2  3    E
3  1    B
3  2    A
3  2    B
3  2    D
3  2    E
3  3    A
3  3    B
3  3    C
3  3    D

And I would like to have a variable 'first', like this:

ID Time Category First 
1  1    A        1
1  1    B        1
1  1    C        1
1  1    D        1
1  2    B        0
1  2    D        0
1  2    E        1
1  3    A        0
1  3    B        0
1  3    E        0
2  1    B        1
2  1    D        1
2  1    E        1
2  2    B        0
2  2    E        0
2  3    A        1
2  3    E        0
3  1    B        1
3  2    A        1 
3  2    B        0
3  2    D        1
3  2    E        1
3  3    A        0
3  3    B        0
3  3    C        1
3  3    D        0

This seemed like a relatively simple problem. However, my problem is that I have a lot of different categories, so I think I need some kind of loop and I have some difficulties with figuring out how to set up a loop. Could you maybe suggest me how to deal with this?

Kind regards,
Frank

[Mike Lacy]

I believe this will work for you:

bysort ID Category (Time): gen byte first = (_n ==1)

[Frank van Laan]

I believe this will work for you:

bysort ID Category (Time): gen byte first = (_n ==1)

Great! This does work indeed. Much simpler than I thought. Thanks a lot.