Re: st: Different results with the same code

[Estrella Gomez <estrellastata@gmail.com>]

I do the collapse by country and orig; and the variables I include in
(firstnm) do not vary by country and orig, that's why I thougth that
picking the first value in each case would be enough; because it
should be equal to the rest of cases in that pair. Is not like that?

Thanks,
Estrella


2014-02-10 11:08 GMT+01:00 Nick Cox <njcoxstata@gmail.com>:
> Wrong way round: -collapse- reports (firstnm) as it finds them; it's
> the sorting that includes some arbitrariness.
>
> But evidently you have different values on variables for which you
> select (firstnm), so why do you want to pick the first non-missing and
> what sort order do you want?
>
> Nick
> njcoxstata@gmail.com
>
>
> On 10 February 2014 09:59, Estrella Gomez <estrellastata@gmail.com> wrote:
>> Hi, Nick
>>
>> I have tried sorting just before the collapse and it happens the same
>> thing. Does (firstnm) use random values each time then?
>>
>> Thank you,
>> Estrella
>>
>> 2014-02-10 10:41 GMT+01:00 Nick Cox <njcoxstata@gmail.com>:
>>> Contrary to your claim, I would point at this:
>>>
>>> Which values are (firstnm) is likely to depend on the exact sort order
>>> of your data and you are sorting before you -collapse-.
>>>
>>> As Phil Schumm often explains, you could get consistent results by
>>> insisting on stable sorting, but that would be hiding a bug. There's
>>> evidently some arbitrariness that is better fixed directly.
>>> Nick
>>> njcoxstata@gmail.com
>>>
>>>
>>> On 10 February 2014 09:07, Estrella Gomez <estrellastata@gmail.com> wrote:
>>>> Dear Statalisters
>>>>
>>>> I am running a code and I have realized that every time I run it the
>>>> results (the coefficients and the standard errors) are different. This
>>>> is the code:
>>>>
>>>> clear all
>>>> use "itunes_grav_song", clear
>>>> sort id country orig
>>>>
>>>> egen  nb_id=tag(id)
>>>> bysort orig: egen nr_orig=sum(nb_id)
>>>> bysort orig country: egen nr_dest=sum(available)
>>>> gen avail_share=(nr_dest/nr_orig)
>>>> collapse (count) nr_songs=id (firstnm) contig comlang ldist
>>>> avail_share, by(country orig)
>>>> encode country, gen(d_id)
>>>> encode orig, gen(o_id)
>>>> gen home=country==orig
>>>>
>>>> reg avail_share ldist comlang home i.d_id i.o_id
>>>>
>>>>
>>>> I have checked and after the collapse I obtain every time the same
>>>> dataset, so I don't know what can be the reason
>>>>
>>>> Thanks for any help!
>>>> Estrella
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