Re: st: RE: Duplicate observations

[Nick Cox <njcoxstata@gmail.com>]

Joe is right.

Away from -gsort- a minus sign in a varlist acts as a hyphen,

Good catch!
Nick
njcoxstata@gmail.com


On 10 March 2014 18:58, Joe Canner <jcanner1@jhmi.edu> wrote:
> Emanuele,
>
> Nick provided a good solution to your problem, but it's probably worth noting why you had a problem to begin with.
>
> The statement:
>
> by reporter partner year (x_1 -date), sort: gen duplicates=_n
>
> is probably not doing what you want it to do.  It looks like you want to sort by x_1 (ascending) and date (descending).  However, as far as I am aware, the minus sign to indicate a descending sort can only be used in a -gsort- command.  In this context the minus is sign is interpreted as a hyphen and thus "x_1 -date" is a variable list (variables x_1 through date).  Accordingly, it is not sorting in descending date order, which results in the problem you noted.
>
> If you need to do something like this in the future and Nick's solution doesn't apply, try the following:
>
> gsort reporter partner year x_1 -date
> bysort reporter partner year:  gen duplicates=_n
>
> Regards,
> Joe Canner
> Johns Hopkins University School of Medicine
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of emanuele mazzini
> Sent: Monday, March 10, 2014 2:31 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: Duplicate observations
>
> Hello to everybody,
>
> I have an issue about duplicate observations that I find puzzling to solve.
> I have data on country-pairs by year and I am interested in two
> specific variables, a date and, say a variable which I call x_1.
>
> Specifically, my data look like this :
>
> reporter  partner   year       date         x_1
>
> Albania  Austria   1980   6dec1980     n_1
> Albania  Austria   1980  15nov1980    n_1
> .         .        .
> .         .        .
> .         .        .
>
> As you may have noticed observations differ amongst them only by date
> and I need to drop them so as to keep the most recent one (hence, in
> this case the second one).
>
> I ran the following commands:
>
> duplicates tag reporter partner year, generate(dup)
>
> by reporter partner year (x_1 -date), sort: gen duplicates=_n
>
> so as to be able to identify duplicates and then - among those with
> dup >0 - drop those for which duplicates > 1.
> This method was suggested in this thread (I take this opportunity to
> thank again), but it seems not to work for some observations.
> Take, for instance the following example:
>
> reporter partner    year      date         x_1    dup     duplicates
> Albania Germany 1967 08apr1967    n_1      1           1
> Albania Germany 1967 17dec1967   n_1      1           2
>
> As you may notice, Stata identifies the observation occurred the
> 17dec1967 as those with duplicates > 1 (which will then be dropped),
> while I would have expected Stata to make the opposite.
>
> Can anyone explain me why and, possibly, tell me how to deal with such issue?
>
> Thank you very much in advance,
>
> Emanuele
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