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Re: st: tag by category


From   Estrella Gomez <estrellastata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: tag by category
Date   Fri, 4 Oct 2013 10:33:45 +0200

Thank you very much!

2013/10/4 Nick Cox <njcoxstata@gmail.com>:
> egen tag = tag(id country)
> egen ntags = total(tag), by(country)
> tabdisp country, cell(ntags)
>
> The principle is kick-yourself-easy. The first command assigns 1 to
> precisely one observation for each combination of -id- and -country-
> and 0 otherwise. The second command adds those values up by -country-.
> Adding 1s, one for each instance, is usually just called counting. The
> 0s naturally do not affect the total.
>
> For the fullest (because only) review of this generic problem, see
>
> 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
>
> which is downloadable. See
> http://www.stata-journal.com/sjpdf.html?articlenum=dm0042
>
> Nick
> njcoxstata@gmail.com
>
> On 4 October 2013 08:42, Estrella Gomez <estrellastata@gmail.com> wrote:
>
>> I have a panel that contains 16030 different ids per 28 countries. I
>> would like to know how many different ids do I have per country,
>> because not all the ids are available in all countries. I have tried
>> the command:
>>
>> by country: egen tag=tag(id)
>>
>> But tag is not compatible with by. Does anybody know any easy way of doing this?
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