Beginner question - sum multiple edges

[Kaepke, Marc]

Hi,

how can I sum and reduce multiple edges in my entire graph?

e.g. my input graph looks like (source-ID, target-ID, value): 
(1, 2, 30)
(1, 2, 10)
(2, 1, 55)

And I need:
(1, 2, 40)
(2, 1, 55)


Thanks!
Marc