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# RE: st: RE: Merge problem

 From Erik Aadland <[email protected]> To "[email protected]" <[email protected]> Subject RE: st: RE: Merge problem Date Fri, 4 Oct 2013 12:10:32 +0000

```Dear Joe.

The number of periods is not completely fixed in dataset (B).
In year == 1, I have periods (1-8)
In year == 2, I have periods (9-17)
In year == 3, I have periods (18-28)
In year == 4, I have periods (29-39)
In year == 5, I have periods (40-50)
In year == 6, I have periods (51-61)
In year == 7, I have periods (62-72)
In year == 8, I have periods (73-75)

So a total of 75 periods spread over 8 years in dataset (B).

Sincerely,
Erik.

> From: [email protected]
> To: [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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```