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Re: st: RE: Merge issues - m:m not returning all matches


From   Aaron Legler <aaron.legler@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: Merge issues - m:m not returning all matches
Date   Fri, 20 Jan 2012 10:46:11 -0500

Joinby works great - thanks Nick.

Aaron

On Fri, Jan 20, 2012 at 10:40 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> Also, your problem sounds more like one for -joinby-.
>
> Nick
> n.j.cox@durham.ac.uk
>
>
> -----Original Message-----
> From: Nick Cox
> Sent: 20 January 2012 15:36
> To: 'statalist@hsphsun2.harvard.edu'
> Subject: RE: Merge issues - m:m not returning all matches
>
> On m:m merges: see the thread last week starting with
>
> http://www.stata.com/statalist/archive/2012-01/msg00370.html
>
> However, please ignore my post in that thread: it missed the point, which is well explained by others.
>
> Nick
> n.j.cox@durham.ac.uk
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Aaron Legler
> Sent: 20 January 2012 15:25
> To: statalist@hsphsun2.harvard.edu
> Subject: st: Merge issues - m:m not returning all matches
>
> I am having an issue with merge -
>
> I have one dataset with patient_id and censustract, and another file with
> censustract and distance to 16 locations
>
> When I perform the merge I am not getting all the possible matches:
>
> This is the original patient with 2 records
>
>    patiennum         geoid    svc_date
>       12345   25009205500   01 Aug 09
>       12345   25009205500   05 Sep 10
>
> after the merge:  merge m:m geoid using chc.censustract.dist.dta
>
> I should get 32 records (2 patient records x 16 locatons) but I'm only
> getting 16:
>
>    patien~m         geoid    svc_date   km_to_~c   hosp        _merge
>       12345   25009205500   01 Aug 09     13.701      2   matched (3)
>       12345   25009205500   05 Sep 10     15.144      1   matched (3)
>       12345   25009205500   05 Sep 10     15.144      5   matched (3)
>       12345   25009205500   05 Sep 10     15.144     13   matched (3)
>       12345   25009205500   05 Sep 10     15.144     14   matched (3)
>       12345   25009205500   05 Sep 10     19.156     12   matched (3)
>       12345   25009205500   05 Sep 10     19.156     16   matched (3)
>       12345   25009205500   05 Sep 10     20.407      3   matched (3)
>       12345   25009205500   05 Sep 10     20.407      4   matched (3)
>       12345   25009205500   05 Sep 10     20.407      6   matched (3)
>       12345   25009205500   05 Sep 10     20.407      8   matched (3)
>       12345   25009205500   05 Sep 10     20.407     11   matched (3)
>       12345   25009205500   05 Sep 10     20.407     15   matched (3)
>       12345   25009205500   05 Sep 10     25.031      9   matched (3)
>       12345   25009205500   05 Sep 10     25.038      7   matched (3)
>       12345   25009205500   05 Sep 10     25.583     10   matched (3)
>
> It seems like the system isn't recognizing the differences in svc_date and
> just running 1 match.
>
> I checked to ensure the geoids are the same:
>
> . tab geoid
>      geoid |      Freq.     Percent        Cum.
> ------------+-----------------------------------
>   2.50e+10 |         16      100.00      100.00
> ------------+-----------------------------------
>      Total |         16      100.00
>
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