Neo4j Cypher: Match and Delete the subgraph based on value of node property

Question

Suppose I have 3 subgraphs in Neo4j and I would like to select and delete the whole subgraph if all the nodes in the subgraph matching the filtering criteria that is each node's property value <= 1. However if there is atleast one node within the subgraph that is not matching the criteria then the subgraph will not be deleted.

In this case the left subgraph will be deleted but the right subgraph and the middle one will stay. The right one will not be deleted even though it has some nodes with value 1 because there are also nodes with values greater than 1.

userids and values are the node properties.

I will be thankful if anyone can suggest me the cypher query that can be used to do that. Please note that the query will be on the whole graph, that is on all three subgraphs or more if there are anymore.

Answer 1

Thanks for the clarification, that's a tricky requirement, and it's not immediately clear to me what the best approach is that will scale well with large graphs, as most possibilities seem to be expensive full graph operations. We'll likely need to use a few steps to set up the graph for easier querying later. I'm also assuming you mean "disconnected subgraphs", otherwise this answer won't work.

One start might be to label nodes as :Alive or :Dead based upon the property value. It should help if all nodes are of the same label, and if there's an index on the value property for that label, as our match operations could take advantage of the index instead of having to do a full label scan and property comparison.

MATCH (a:MyNode)
WHERE a.value <= 1
SET a:Dead

And separately

MATCH (a:MyNode)
WHERE a.value > 1
SET a:Alive

Then your query to mark nodes to delete would be:

MATCH (a:Dead)
WHERE NOT (a)-[*]-(:Alive)
SET a:ToDelete

And if all looks good with the nodes you've marked for delete, you can run your delete operation, using apoc.periodic.commit() from APOC Procedures to batch the operation if necessary.

MATCH (a:ToDelete)
DETACH DELETE a

If operations on disconnected subgraphs are going to be common, I highly encourage using a special node connected to each subgraph you create (such as a single :Cluster node at the head of the subgraph) so you can begin such operations on :Cluster nodes, which would greatly speed up these kind of queries, since your query operations would be executed per cluster, instead of per :Dead node.