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# st: RE: Merge problem

 From Joe Canner <[email protected]> To "[email protected]" <[email protected]> Subject st: RE: Merge problem Date Fri, 4 Oct 2013 11:56:06 +0000

```Erik,

If there are a fixed, known number of periods per year, you can use -expand- in dataset (A).  Suppose (as in your example) there are 4 periods (1,2,3,4):

. expand 3
. bys year firm_id: gen period_id=_n

However, if the number of periods depends on some information in dataset (B), that's a different story.  If so, please provide more information on how the number of periods is to be determined.

Regards,
Joe Canner
Johns Hopkins University School of Medicine

________________________________________
From: [email protected] [[email protected]] on behalf of Erik Aadland [[email protected]]
Sent: Friday, October 04, 2013 4:18 AM
To: [email protected]
Subject: st: Merge problem

Dear Statalist.

I have two datasets. One dataset (A) contains the variables "year" and "firm_id". A firm observation ("firm_id") occurs only once in a given "year".

The other dataset (B) contains the variables "year", "period_id" and "firm_id". There are many periods within a given year, and firm observations ("firm_id") are nested within periods. So a given firm ("firm_id") may occur several times in a given year. The firms in (A) are not the same firms as in (B). The structure of (A) and (B) are as follows.

(A):
year    firm_id
2003    1
2003    2
2003    3
2003    4
2004    1
2004    2
2004    5
2004    6

(B):
year    period_id       firm_id
2003    1                       11
2003    1                       12
2003    2                       13
2003    2                       14
2003    2                       11
2004    3                       11
2004    3                       12
2004    3                       15
2004    4                       16
2004    4                       17

I want to merge the firms in (A) into (B) such that the firms in (A) in a given year occur in all periods for the corresponding year in (B). The problem is that I don't have "period_id" for my firm observations in (A).

Is there a smart way to handle this problem? I use Stata 12.

Any input on this would be much appreciated.

Sincerely,
Erik
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