calculating distance in a loop using 'spdistance' in STATA 15

[Mudassira Sarfraz]

Dear Statalisters

I have shapefile containing information about the geographic coordinates of all the districts in Pakistan. I am required to have a variable of the distance between a border district and the rest of all the districts. I am using STATA 15's 'spdistance' command to calculate it. As the syntax for 'spdistance' returns the distance between two district IDs whereas I want to calculate the distance between 93 districts. Is there any way I can do it in a loop? I am writing the codes here as I am not sure how to use 'dataex' with shapefile.

capture drop distance
gen distance=.
local id 20 54 94 95 99 101
spdistance `id' 96 (* where 96 is the id for border district which will remain fixed)
replace distance=r(distance) if distt_id==`id'

however, this code returns an error i.e
94 95 99 101 96 found where nothing expected
r(198);

[Phil Bromiley]

You didn't get a quick answer. You'll increase your chances of a useful answer by following the FAQ on asking questions - provide Stata code in code delimiters, readable Stata output, and sample data using dataex.

I don't use spdistance, but the documentation is clear it works with two id's. So, set up a loop over id's and then save each of the distances where ever you want them saved. Often this is done by setting up a variable with all empty values and replacing the appropriate values after each invocation of the procedure (spdistance).

[Mudassira Sarfraz]

Dear Phil

Many thanks for your reply. Yes, you are right I should have provided Stata code and output using dataex.
However, as you advised, I tried to loop over id's and save the distance in a new variable "distance". The following code I used and it worked.

capture drop distance
gen distance=.
local j 96 /*96 is the code for border district*/
local id 54 94 95 99 101 104
forvalues w=1/6{
local i : word `w' of `id'
spdistance `i' `j'
local d=r(distance)
replace distance=`d' if distt_id==`i'
}

Thanks.