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st: Re: st: RE: Calculatin​g the shortest distances between observatio​ns (based on longitude and latitude)


From   Rüdiger Vollmeier <ruediger.vollmeier@googlemail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: st: RE: Calculatin​g the shortest distances between observatio​ns (based on longitude and latitude)
Date   Fri, 3 Feb 2012 11:02:58 +0100

Thanks for the insightful replies.

Nearstat actually seems to look pretty much like what I ve been
looking for. However, it seems that there are some problems with the
STATA versions. I am using STATA 11 and it is stated that nearstat can
be used by STATA 10 or higher.

However, whenever I run nearstat, I get the following error message:
(nearstat_calcdist() in lnearstat, compiled by Stata 12.0, is too new
to be run by
this version of Stata and so was ignored)
                 <istmt>:  3499  nearstat_calcdist() not found
r(3499);

Confusing right? Does anybody know why this happens?

Ruediger.

2012/2/2 P. Wilner Jeanty <pwjeanty@gmail.com>:
> 2012/2/2 Rüdiger Vollmeier <ruediger.vollmeier@googlemail.com>:
>> Hello guys,
>>
>> I want to calculate the shortest distances between observations based
>> on the coordinates (latitude, longitude). I have adapted a simple
>> version from N. Cox's nearest neighbor search which was presented here
>> some time ago. In contrast to that, I want to calulate not only the
>> shortest but also the second shortest (third, and so on) distances.
>>
>> Here is a simplified structure of the dataset:
>>
>> observation_type        country year    latitude        longitude
>> 1                               Albania 2010    42.07972        19.52361
>> 1                               Albania 2010    42.15028        19.66389
>> 1                               Albania 2010    42.01667        19.48333
>> 2                               Albania 2010    39.95   20.28333
>> 2                               Albania 2010    42.08417        20.42
>>
>> I want to calculate the smallest distances for a given observation of
>> observation_type=1 to an observation of type=2 for a given year in a
>> given country. Here is the code (all variables are generated of the
>> form gen bank_1_dist_1 =.)
>>
>> * Shortest distance
>> local n = _N
>>                forval i = 1/`n' {
>>                        forval j = 1/`n' {
>>                        if  (`i' != `j') & (observation_type[`i']==1) &
>> (observation_type[`j']==2) &
>> (country_number[`i']==country_number[`j']) & (year[`i']==year[`j']) {
>>                        local d  = (latitude[`i'] - latitude[`j'])^2 + (longitude[`i'] -
>> longitude[`j'])^2
>>                        replace bank_2010_1_`j'=`d' in `i'
>>                        if `d' < bank_1_dist_1[`i'] {
>>                                                replace bank_1_dist_1 = `d' in `i'
>>                                                replace bank_1_id_1 = `j' in `i'
>>                                        }
>>                        }
>>                }
>>        }
>> * Second shortest distance
>> local n = _N
>>                forval i = 1/`n' {
>>                        forval j = 1/`n' {
>>                        if  (`i' != `j') &(observation_type[`i']==1)
>> &(observation_type[`j']==2)
>> &(country_number[`i']==country_number[`j']) &(year[`i']==year[`j']) {
>>                        local d2  = (latitude[`i'] - latitude[`j'])^2 + (longitude[`i'] -
>> longitude[`j'])^2
>>                        if (`d2' > bank_1_dist_1[`i']) & (`d2' < bank_1_dist_2[`i']) {
>>                                                replace bank_1_dist_2 = `d2' in `i'
>>                                                replace bank_1_id_2 = `j' in `i'
>>                                        }
>>                        }
>>
>>                }
>>        }
>>
>> Here is the problem: The shortest distance seems to be well
>> calculated. However, the second smallest distance is not calculated
>> correctly (sometimes it takes on the same value as the shortest
>> distance and only sometimes it is the actual shortest distance). Do
>> you know why? Do you have any suggestions for improvement?
>>
>> Thanks in advance.
>> Ruediger
>
>
> For what Ruediger wants to do, his best bet may be -nearstat-. He can
> install -nearstat- by typing:
>
> ssc install nearstat, all
>
>
> Best regards,
>
>
> Wilner
>
> -------------------------------------
> P. Wilner Jeanty
> Rice University
> Email: pwjeanty@rice.edu
>
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