Re: st: Identify Neighbor Regions with Latitudes and Longitudes‏

[Brendan Halpin <brendan.halpin@ul.ie>]

On Sun, Sep 23 2012, ��wrote:

> Hello, Brendan,
>
> Thanks a lot for replaying. With distance matrix, I am not quite
> understand how to figure up which cities are the neighbor cities for a
> particular cities. Are you talking about the nearest city? I need all
> the adjoining cities for each one. 

If you can define clearly what you mean by "adjoining", this is easy
enough. Say you want to identify the nearest three cities to each city.
If your data has a row for each city with distances to each other city,
you can identify the nearest N cities easily enough:

----------------------------------------------------------------------
// Data containing city id and distance to each of 10 cities
// Note distance to self is included
input id d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 
    1     0    89    83   132   165    19   151    14   153   134  
    2    89     0    54   159    73   165    69    94    46   157  
    3    83    54     0    95   113    72    64    94    34    86  
    4   132   159    95     0    75    80   174    91    80    98  
    5   165    73   113    75     0    50   127   138   119   150  
    6    19   165    72    80    50     0    89    67    36    99  
    7   151    69    64   174   127    89     0    99   129    91  
    8    14    94    94    91   138    67    99     0   113    47  
    9   153    46    34    80   119    36   129   113     0   104  
   10   134   157    86    98   150    99    91    47   104     0  
end

// Reshape long
reshape long d, i(id) j(city)

// Sort by distance within ID, keep the lowest three distances to other cities
sort id d
drop if id==city
by id: keep if _n<=3

// Re-initialise the reshape j-counter and reshape wide
by id: gen t = _n
reshape wide d city, i(id) j(t)
----------------------------------------------------------------------


Brendan

-- 
Brendan Halpin,   Department of Sociology,   University of Limerick,   Ireland
Tel: w +353-61-213147  f +353-61-202569  h +353-61-338562;  Room F1-009 x 3147
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