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st: counting unique ids
I have a cross-section panel data that is unbalanced. For instance:
id year x1
111 1999 3
111 2000 5
111 2001 6
123 2000 4
123 2001 2
For the above example, there are 2 unique ids (111 and 123). Since my
dataset has over 6000 observations, what commands should I use to generate a
count of unique ids?
Any help would be appreciated. Thanks!
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