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Re: st: Duplicate observations
From
Nick Cox <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: Duplicate observations
Date
Mon, 10 Mar 2014 18:35:04 +0000
Duplicates are a red red herring herring here.
(http://en.wikipedia.org/wiki/Red_herring may help internationally.)
To keep the last only
bysort reporter partner (date) : keep if _n == _N
Nick
[email protected]
On 10 March 2014 18:30, emanuele mazzini <[email protected]> wrote:
> 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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