apoc.refactor.mergeNodes choose the result properties randomly

[neo-technology-build-agent]

Issue by PeterKazmirsky
Tuesday Feb 19, 2019 at 15:58 GMT
Originally opened as neo4j-contrib/neo4j-apoc-procedures#1107

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Guidelines
Imagine that I have user cluster consisting of user ids from different data sources and all users are connected to one Root node. In case that user cluster contains more than one Root node I want to merge this Root nodes to one. For finding the Root nodes in cluster I am using apoc.path.subgraphNodes and the resulting Root nodes I am sending to apoc.refactor.mergeNodes to merge them to one Root node. I also set properties to procedure: mergeRels:true, properties:'overwrite'

Actual Behavior
I cannot influence in what order roots get into procedure apoc.refactor.mergeNodes, so after merging the result Root node and his relationships properties will have random properties.

Expected Behavior
I would like you to consider to add feature to apoc.refactor.mergeNodes where I can tell for example that for merging property "count" choose highest one. Or for "date" property choose latest one.
Thank you.

Versions
Neo4j 3.5.2
Apoc library 3.5.0.1

[neo-technology-build-agent]

Comment by jexp
Tuesday Feb 19, 2019 at 18:16 GMT

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MergeNodes uses collection order
You can use apoc.coll.sort to sort by a key you like

[neo-technology-build-agent]

Comment by PeterKazmirsky
Wednesday Feb 20, 2019 at 07:46 GMT

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Thanks. But what about relationships. I recently created ticket where I asked to overwrite properties in relationships in procedure mergeNodes. And now I would like to sort properties of relationships and choose the proper one before merging. Is there any solution for that as well ?

[neo-technology-build-agent]

Comment by vga91
Thursday Jun 24, 2021 at 15:06 GMT

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With a simple dataset like:

create (r:Root), (r2:Root) with r, r2
create (r2)<-[:MyRel {prop: "prop1"}]-(n1:User{value:'node1'})-[:MyRel {prop: "prop11"}]->(r)
create (r2)<-[:MyRel {prop: "prop2"}]-(n2:User{value:'node2'})-[:MyRel {prop: "prop22"}]->(r)
create (r2)<-[:MyRel {prop: "prop3"}]-(n3:User{value:'node3'})-[:MyRel {prop: "prop33"}]->(r)

This could be solved in this way:

Match (r:Root) 
with collect(r) as nodes    // I CAN ORDER NODES HERE
CALL apoc.refactor.mergeNodes(nodes, {properties:'overwrite'}) YIELD node // NO mergeRels:true
WITH node 
match (node)-[r]-(user:User)
with user, collect(r) as rels   // I CAN ORDER RELS HERE
call apoc.refactor.mergeRelationships(rels, {properties: 'DISCARD'}) yield rel return rel
// with {properties: 'DISCARD'} we choose the first in order of appearance, otherwise the last

[gem-neo4j]

Closing as a workaround was produced and there has been no further comment in over 2 years