Merge Nodes

We can merge a list of nodes onto the first one in the list. All relationships are merged onto that node too. We can specify the merge behavior for properties globally and/or individually.

MATCH (p:Person)
WITH p ORDER BY p.created DESC // newest one first
WITH p.email AS email, collect(p) as nodes
CALL apoc.refactor.mergeNodes(nodes, {properties: {
    name:'discard',
    age:'overwrite',
    kids:'combine',
    `addr.*`: 'overwrite',
    `.*`: 'discard'
}})
YIELD node
RETURN node

Below are the config options for this procedure: These config option also works for apoc.refactor.mergeRelationships([rels],{config}).

type operations

discard

the property from the first node will remain if already set, otherwise the first property in list will be written

overwrite / override

last property in list wins

combine

if there is only one property in list, it will be set / kept as single property otherwise create an array, tries to coerce values

In addition, mergeNodes supports the following config property:

type operations

mergeRels

true/false" : give the possibility to merge relationships with same type and direction.

Relationships properties are managed with the same nodes' method, if properties parameter isn’t set relationships properties are combined.

Example Usage

The examples below will help us learn how to use these procedures.

Same start and end nodes

The following creates a graph containings relationships that have the same start and end nodes
CREATE (n1:Person {name:'Tom'}),
(n2:Person {name:'John'}),
(n3:Company {name:'Company1'}),
(n5:Car {brand:'Ferrari'}),
(n6:Animal:Cat {name:'Derby'}),
(n7:City {name:'London'}),

(n1)-[:WORKS_FOR {since:2015}]->(n3),
(n2)-[:WORKS_FOR {since:2018}]->(n3),
(n3)-[:HAS_HQ {since:2004}]->(n7),
(n1)-[:DRIVE {since:2017}]->(n5),
(n2)-[:HAS {since:2013}]->(n6);
return *;
apoc.refactor.mergeNodes.createDataSetFirstExample
The following merges John and Tom into a single node:
MATCH (a1:Person{name:'John'}), (a2:Person {name:'Tom'})
WITH head(collect([a1,a2])) as nodes
CALL apoc.refactor.mergeNodes(nodes,{properties:"combine", mergeRels:true})
YIELD node
RETURN count(*)

If we execute this query, it will result in the following graph:

apoc.refactor.mergeNodes.resultFirstExample

Since we have relationships with same start and end nodes, relationships are merged and properties are combined.

Different start and end nodes

The following creates a graph containings relationships that have different start or end nodes:
Create (n1:Person {name:'Tom'}),
(n2:Person {name:'John'}),
(n3:Company {name:'Company1'}),
(n4:Company {name:'Company2'}),
(n5:Car {brand:'Ferrari'}),
(n6:Animal:Cat {name:'Derby'}),
(n7:City {name:'London'}),
(n8:City {name:'Liverpool'}),
(n1)-[:WORKS_FOR{since:2015}]->(n3),
(n2)-[:WORKS_FOR{since:2018}]->(n4),
(n3)-[:HAS_HQ{since:2004}]->(n7),
(n4)-[:HAS_HQ{since:2007}]->(n8),
(n1)-[:DRIVE{since:2017}]->(n5),
(n2)-[:HAS{since:2013}]->(n6)
return *;
apoc.refactor.mergeNodes.createDataSetSecondExample
The following merges John and Tom into a single node:
MATCH (a1:Person{name:'John'}), (a2:Person {name:'Tom'})
WITH head(collect([a1,a2])) as nodes
CALL apoc.refactor.mergeNodes(nodes,{
    properties:"combine",
    mergeRels:true
})
YIELD node
RETURN count(*)

If we execute this query, it will result in the following graph:

apoc.refactor.mergeNodes.resultSecondExample
apoc.refactor.mergeNodes.resultSecondExampleData

Since we have relationships with different end nodes, all relationships and properties are maintained.