st: Re: question about ids in a group

[Pat R <profanepolicy@gmail.com>]

Thank you Joseph, this is exactly what I wanted! Now to figure out how
exactly it works :)

Pat

On Sat, Mar 19, 2011 at 11:33 PM, Joseph Coveney <jcoveney@bigplanet.com> wrote:
>
> Pat R wrote:
>
> 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)
>
> --------------------------------------------------------------------------------
>
> If I understand you correctly, then it would be something like that illustrated
> below.  If that's not what you want, then write back to the list with a fourth
> column in you example that shows just what you want as the result.
>
> Joseph Coveney
>
> . version 11.1
>
> .
> . clear *
>
> . set more off
>
> .
> . input long (QID Year PersonID)
>
>              QID          Year      PersonID
>  1.  1 2009  3
>  2.  1 2009  4
>  3.  2 2009  9
>  4.  2 2009 10
>  5.  2 2010  9
>  6.  2 2010 10
>  7.  2 2009 11
>  8. end
>
> .
> . *
> . * Begin Here
> . *
> . bysort QID PersonID: generate long new_id = _n == 1
>
> . quietly by QID: replace new_id = sum(new_id)
>
> . list, noobs sepby(QID)
>
>  +--------------------------------+
>  | QID   Year   PersonID   new_id |
>  |--------------------------------|
>  |   1   2009          3        1 |
>  |   1   2009          4        2 |
>  |--------------------------------|
>  |   2   2010          9        1 |
>  |   2   2009          9        1 |
>  |   2   2009         10        2 |
>  |   2   2010         10        2 |
>  |   2   2009         11        3 |
>  +--------------------------------+
>
> . exit
>
> end of do-file
>
>
>

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