Is it possible to merge edges in Neo4j in such a way that the values of the properties add up?
Hello @marcelix161 
Have a look at apoc.refactor.mergeRelationships() function in the APOC plugin. You can have more configuration here, (same as apoc.refactor.mergeNodes() function).
Regards,
Cobra
I deleted the previous post as it had an error. It did not work correctly when a node had multiple relationships to multiple nodes. I had to update the 'with' clause to include the nodes at each end of the relationships, so the grouping of the relationships was correct.
match(n:Node)-[r:REL]->(m:Node)
with n, m, sum(r.w) as total, collect(r) as relationships
where size(relationships) > 1
with total, head(relationships) as keep, tail(relationships) as delete
set keep.w = total
foreach(r in delete | delete r)
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Hi Gary,
Thank you for your solution! You've helped me a lot!