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st: SPHDIST, creating pairs


From   "Tomeka Davis" <soctmd@langate.gsu.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: SPHDIST, creating pairs
Date   Thu, 25 Feb 2010 16:26:54 -0500

Hello -

I am trying to calculate distance between two points using longitude and latitude data.  I have come across 2 different Stata commands to do this - SPHDIST and VICENTY.  I have not been able to install the VICENTY command.  It appears from previous StataList posts that there might be problems associated with it and therefore it is temporarily unavailable (right?).

Although I have longitude and latitude data, I am not sure how to create the pairs necessary to calculate distance with SPHDIST.   I would like to calculate distance from a each public school in a district to all the other private schools in the same district.  My data SHOULD look like this:

District ID     Public School ID       Private School ID        Public Longitude         Public Latitude       Private Latitude        Private Longitude
1                          A                             1  
1                          A                             2 
1                          B                             1
1                          B                             2
1                          B                             3
1                          B                             4
2                          C                             1    
2                          C                             2
2                          C                             3
2                          D                             1
2                          D                             2  

I initially had two separate files; one with public school data and one with private school data.  I appended the public school file and tacked on the private school data.  


NOW the data looks something like this 

Distric ID     School ID       Public School     Private School         Latitude       Longitude
1                          A                       Y                     N
1                          A                       Y                     N
1                          B                       Y                     N
1                          B                       Y                     N   
1                          B                       Y                     N
1                          B                       Y                     N
2                          C                      N                     Y
2                          C                      N                     Y
2                          C                      N                     Y
2                          D                      N                     Y
2                          D                      N                     Y 



But I want to pair each public school with each private school.

So far, I have figured out how to produce a data set pairing ALL schools within each district; this would pair public schools within a district with other public schools in the same district (using a an FAQ page from 2005 written by Nick Cox titled "Expanding datasets to all possible pairs").  However, I don't want this.  I only want to pair each public school with each private school in the same district.


How do I accomplish this?

I would appreciate any help anyone could offer. Also, any suggestions about the best distance command would be appreciated.


Thank you.


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