st: distance data missing values

[Ermal Hitaj <ermalhitaj@yahoo.com>]

Hi,

I wonder whether somebody could help with the following:
I have trade distance data in a long form. I have missing values as follows.

Exporter Importer Distance
A          B       1000km
B          A          .

I need to substitute the missing values with the distance value from the case where country A is the exporter and B is the importer.
Obviosly, there's a lot of countries (and a lot of products).

Thanks,
E.


      
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