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Re: st: Re: question about ids in a group


From   Nick Cox <[email protected]>
To   [email protected]
Subject   Re: st: Re: question about ids in a group
Date   Sun, 20 Mar 2011 10:22:44 +0000

I wonder if you missed the -unique- option within -egen, rank()-.

Nick

On Sun, Mar 20, 2011 at 3:41 AM, Pat R <[email protected]> wrote:

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

> On Sat, Mar 19, 2011 at 11:33 PM, Joseph Coveney <[email protected]> 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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