Stata command to add all choices, those made and those not made - stata

Question

UPDATE:
I solved the first part of the problem. I created unique ids for each observation:
gen id=_n
Then, I used
fillin id categ
which essentially created what I was looking for.
However, for the rest of the variables (except id and categ), almost all observations are missing. Now, I need your help to duplicate the rest of the variables instead of having them missing.
Just as an example, each observation is associated with a particular week. I am missing most of them. Or another dummy variable indicates whether a purchase was made at a drug or grocery store. Most of them are missing too.
Thanks!
ORIGINAL MESSAGE:
Need your help in Stata!
Each observation in my database is a 1-unit purchase of a beer product made by a customer. These product purchases are categorized unto 8 general categories such that the variable "categ" has values from 1 to 8 (1=import, 2=craft, 3=premium, 4=light, etc).
For my multinomial logit model, I need to observe all categories purchased or not purchased by the customer in each observation.
Assume, this is my initial dataset:
customer id-------beer category-----units purchased
----------1------------------1--------------------- 1
----------2----------------- 3--------------------- 1
----------3 -----------------2 ---------------------1
This is what I am looking for:
customer id-------beer category-----units purchased
----------1------------------1--------------------- 1
----------1 -----------------2 ---------------------0
----------1----------------- 3--------------------- 0
----------2----------------- 1--------------------- 0
----------2----------------- 3--------------------- 1
----------2 -----------------3--------------------- 0
----------3----------------- 1--------------------- 0
----------3----------------- 2--------------------- 0
----------3 -----------------2 ---------------------1
Currently, my dataset is 600,000 obs. After this procedure, I should have 600,000*8=4,800,000 obs.
When constructing this code, it is necessary that all other variables in the dataset are duplicated according to the associated category of beer.
I assume that "fillin" and less likely "expand" might work.
You help will tremendously help.
Thanks!

Answer 1

This is an old question, but i'll post a possible answer if someone else is having this problem.
In this case, you could generate variables for every option of your "choice variable", and after that, apply the reshape long command:
tab beercategory, gen(b)
reshape long b , i(customerid) j(newvarname)
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