st: Network - double back relation

[Simon Falck <sfalckstata@gmail.com>]

Hi Statalist,

Using Stata 13.1 and aiming at a simple descriptive network plot but 
bump into the issue of double back relations among the edges, i.e. some 
of the networks actually double back on themselves. Here is an sample of 
my dataset:
source    target    weight
1    1    1
2    2    1
3    3    3
3    5    3
3    8    3
4    4    1
5    3    3
5    5    16
5    8    3
6    6    1
7    7    1
8    3    3
8    5    3
8    8    21
9    9    1

For instance, there is a relationship between source '3' and target '5', 
and thus also between target '5' and source '3'. My question is how do I 
manage to only keep one way relation between 'source' and 'target', i.e. 
how do I delete (drop) the double back relationship?
I could be noted that double back relationships has been mentioned in an 
earlier discussion: 
http://www.stata.com/statalist/archive/2013-09/msg00142.html
Thanks in advance!

Best,
Simon
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