Re: st: differentiating between groups of records with same date

[Nick Cox <njcoxstata@gmail.com>]

The Stata Journal article I wrote with Gary Longton has extended
discussion of that too. Perhaps the easiest way to approach this is
something like

egen tag = tag(patient_id proc_type surgery_date)

egen nproc = total(tag), by(patient_id surgery_date)

See p.563 of that article. (A key detail is that Stata Journal
articles more than 3 years old are accessible to all, regardless of
whether you or your institution subscribe to the Journal.)

Nick

On Wed, Aug 1, 2012 at 3:52 AM, Tim Evans <Tim.Evans@wmciu.nhs.uk> wrote:
>
> Thanks for this. I don't think I want to go with  -distinct- and -unique- as I want a flag variable permanently in the dataset. I've worked through the examples in http://www.stata.com/support/faqs/data-management/number-of-distinct-observations/, I'm not sure I'm translating this very well to my scenario, but that's probably my fault in how I'm thinking about it. So I'll give it some space before looking at it again.

Nick Cox

> See
>
> FAQ     . . . . . . . . . . . . . . . . . . .  Number of distinct observations
>         . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox and G. Longton
>         10/08   How do I compute the number of distinct observations?
>                 http://www.stata.com/support/faqs/data-management/
>                 number-of-distinct-observations/
>
>
> SJ-12-2 dm0042_1  . . . . . . . . . . . . . . . . Software update for distinct
>         (help distinct if installed)  . . . . . .  N. J. Cox and G. M. Longton
>         Q2/12   SJ 12(2):352
>         options added to restrict output to variables with a minimum
>         or maximum of distinct values
>
> SJ-8-4  dm0042  . . . . . . . . . . . .  Speaking Stata: Distinct observations
>         (help distinct if installed)  . . . . . .  N. J. Cox and G. M. Longton
>        Q4/08   SJ 8(4):557--568
>         shows how to answer questions about distinct observations
>         from first principles; provides a convenience command

On Tue, Jul 31, 2012 at 8:27 AM, Tim Evans <Tim.Evans@wmciu.nhs.uk> wrote:

>> For the following dataset (below) I wish to count the distinct number of proc_type for each patient on a given surgery_date.
>>
>> patient_no      cancer_no       diag_date       surgery_date      proc_type
>>> 9512834         0484360     21may1994       21may1994                 H1
>>> 9512834         0484358    21may1994       21may1994                  H2
>>> 9512834         0483234    26apr2000       21may2000                  H1
>>> 9512834         0483233    26apr2000
>>> 0000012         0000012          21Jan1999        21Jan1999           H3
>>> 0000012         0000013          21Jan1999        21Jan1999           H3
>>> 0000012         0000014          21Jan1999        21Jan1999           H3
>>
>>
>> In my snapshot above, patient_no 000012 has 3 cancers, with a surgery_date of 21Jan1999, but only one proc_type - so my count should be 1. In contrast, patient_number 9512834 has 2 cancers with a surgery_date of 21may1994, and has 2 proc_types on 21may1994 - my count should therefore be 2.
>>
>> Or put another way, for each surgery date, how many unique proc_types did each patient have.
>>

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