Count the number of relationships between a pair of nodes and set it as parameter in Neo4J

Question

I have a graph where a pair of nodes can have several relationships between them. I would like to count this relationships between each pair of nodes, and set it as a parameter of each relationship.

I tried something like:

MATCH (s:LabeledExperience)-[r:NextExp]->(e:LabeledExperience) 
with s, e, r, length(r) as cnt
MATCH (s2:LabeledExperience{name:s.name})-[r2:NextExp{name:r.name}]->(e2:LabeledExperience{name: e.name})
SET r2.weight = cnt

But this set the weight always to one. I also tried:

MATCH ()-[r:NextExp]->() 
    with r, length(r) as cnt
    MATCH ()-[r2:NextExp{name:r.name}]->()
    SET r2.weight = cnt

But this takes too much time since there are more than 90k relationships and there is no index (since it is not possible to have them on edges).

Answer 1

They are always set to 1 because of the way you are counting.

When you group by s, e, r that is always going to result in a single row. But if you collect(r) for every s, e then you will get a collection of all of the :NextExp relationships between those two nodes.

Also, length() is for measuring the length (number of nodes) in a matched path and should not work directly on a relationship.

Match the relationship and put them in a collection for each pair of nodes. Iterate over each rel in the collection and set the size of the collection of rels.

MATCH (s:LabeledExperience)-[r:NextExp]->(e:LabeledExperience) 
WITH s, e, collect(r) AS rels
UNWIND rels AS rel
SET rel.weight = size(rels)