Re: st: Compute distance to all observations in a group

[Fernando Luco <flucoestatalist@gmail.com>]

Thank you Robert, it was just what I was looking for.

On Sat, Feb 25, 2012 at 10:17 AM, Robert Picard <picard@netbox.com> wrote:
> Here's one way to do it using -joinby- to form all pairwise
> combinations of stores within each county and using -geodist-
> (available from SSC) to calculate the distances:
>
> *----------- begin example -------------
> version 12
>
> clear
> input county store  double lat double lon
> 1 1 -18.47785 -70.31808
> 1 2 -18.47846 -70.31757
> 1 3 -18.48126 -70.31446
> 2 1 -20.24057 -70.14498
> 2 2 -20.23462 -70.14281
> 2 3 -20.21667 -70.14654
> 2 4 -20.25699 -70.1329
> 3 1 -23.67862 -70.40953
> 3 2 -23.5791 -70.39053
> end
>
> tempfile main copy
> save "`main'"
>
> rename * *2
> rename county2 county
> save "`copy'"
>
> use "`main'"
> joinby county using "`copy'"
>
> * ssc install geodist
> geodist lat lon lat2 lon2, gen(km2near)
> drop if store == store2
> sort county store km2near store2
> keep county store km2near lat lon
> by county store: gen near = _n
> reshape wide km2near, i(county store) j(near)
> order county store lat lon
> list, noobs sepby(county)
>
> *------------ end example --------------
>
>
>
> On Sat, Feb 25, 2012 at 10:26 AM, Fernando Luco
> <flucoestatalist@gmail.com> wrote:
>> Dear all,
>>
>> I have a data set with the coordinates of all stores in a country,
>> grouped at the county level. I need to compute the distance from one
>> store to all other stores in the same county. In particular, I'm
>> interested in computing, for each store, the distance to the nearest
>> store, the second one, the third and so on. So far, I haven't been
>> able to do so.
>> The number of stores varies by county. The data looks like this
>>
>> County Store  latitude         longitude
>> 1            1    -18.47785     -70.31808
>> 1             2  -18.47846      -70.31757
>> 1             3  -18.48126      -70.31446
>> 2            1  -20.24057        -70.14498
>> 2            2  -20.23462        -70.14281
>> 2            3  -20.21667        -70.14654
>> 2            4  -20.25699        -70.1329
>> 3            1  -23.67862        -70.40953
>> 3            2  -23.5791          -70.39053
>>
>> Because of what I need to do after getting the distances, I would like
>> the data to look as follows
>>
>> County Store latitude longitude distance_to_nearest_store
>> distance_to_second_nearest store ...distance_to_nth_nearest_store.
>>
>> Any ideas on how to do this?
>>
>> Thanks,
>>
>> Fernando
>> *
>> *   For searches and help try:
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>> *   http://www.ats.ucla.edu/stat/stata/
>
> *
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*
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