st: question about ids in a group

[Pat R <profanepolicy@gmail.com>]

Hi all,

I have a panel dataset from which I'm trying to make a smaller dataset
with new identifiers. My (new) dataset is organised this way right
now:

QID    |   Year  |   PersonID

 1       |   2009  |    3
 1       |   2009  |    4
 2       |   2009  |    9
 2       |   2009  |    10
 2       |   2010  |    9
 2       |   2010  |    10
 2       |   2009  |    11

I want to create new identifiers for each person (consistent across
years), starting from 1, within each QID. I tried using the -egen
group- function, but since I cannot combine that with -by-, it creates
unique values which ignore the QID. I tried using -egen rank-, but
that of course skips a rank if two IDs are the same. I'm sure there's
a terribly easy way to do this, but I just can't see it. Can anyone
help? (It's my first time asking a question, so I apologize if I've
left out important information)

Cheers,
Pat
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