I have created a graph db in Neo4j and want to use it for generalization purposes.
There are about 500,000 nodes (20 distinct labels) and 2.5 million relations (50 distinct types) between them.
In an example path : a -> b -> c-> d -> e
I want to find out the node without any incoming relations (which is 'a').
And I should do this for all the nodes (finding the nodes at the beginning of all possible paths that have no incoming relations).
I have tried several Cypher codes without any success:
match (a:type_A)-[r:is_a]->(b:type_A)
with a,count (r) as count
where count = 0
set a.isFirst = 'true'
or
match (a:type_A), (b:type_A)
where not (a)<-[:is_a*..]-(b)
set a.isFirst = 'true'
Where is the problem?!
Also, I have to create this code in neo4jClient, too.
Your first query will only match paths where there is a relationship [r:is_a], so counting r can never be 0. Your second query will return any arbitrary pair of nodes labeled :typeA that aren't transitively related by [:is_a]. What you want is to filter on a path predicate. For the general case try
MATCH (a)
WHERE NOT ()-->a
This translates roughly "any node that does not have incoming relationships". You can specify the pattern with types, properties or labels as needed, for instance
MATCH (a:type_A)
WHERE NOT ()-[:is_a]->a
If you want to find all nodes that have no incoming relationships, you can find them using OPTIONAL MATCH:
START n=node(*)
OPTIONAL MATCH n<-[r]-()
WITH n,r
WHERE r IS NULL
RETURN n
Related
I have a graph of nodes with a relationship NEXT with 2 properties sequence (s) and position (p). For example:
N1-[NEXT{s:1, p:2}]-> N2-[NEXT{s:1, p:3}]-> N3-[NEXT{s:1, p:4}]-> N4
A node N might have multiple outgoing Next relationships with different property values.
Given a list of node names, e.g. [N2,N3,N4] representing a sequential path, I want to check if the graph contains the nodes and that the nodes are connected with relationship Next in order.
For example, if the list contains [N2,N3,N4], then check if there is a relationship Next between nodes N2,N3 and between N3,N4.
In addition, I want to make sure that the nodes are part of the same sequence, thus the property s is the same for each relationship Next. To ensure that the order maintained, I need to verify if the property p is incremental. Meaning, the value of p in the relationship between N2 -> N3 is 3 and the value p between N3->N4 is (3+1) = 4 and so on.
I tried using APOC to retrieve the possible paths from an initial node N using python (library: neo4jrestclient) and then process the paths manually to check if a sequence exists using the following query:
q = "MATCH (n:Node) WHERE n.name = 'N' CALL apoc.path.expandConfig(n {relationshipFilter:'NEXT>', maxLevel:4}) YIELD path RETURN path"
results = db.query(q,data_contents=True)
However, running the query took some time that I eventually stopped the query. Any ideas?
This one is a bit tough.
First, pre-match to the nodes in the path. We can use the collected nodes here to be a whitelist for nodes in the path
Assuming the start node is included in the list, a query might go like:
UNWIND $names as name
MATCH (n:Node {name:name})
WITH collect(n) as nodes
WITH nodes, nodes[0] as start, tail(nodes) as tail, size(nodes)-1 as depth
CALL apoc.path.expandConfig(start, {whitelistNodes:nodes, minLevel:depth, maxLevel:depth, relationshipFilter:'NEXT>'}) YIELD path
WHERE all(index in range(0, size(nodes)-1) WHERE nodes[index] = nodes(path)[index])
// we now have only paths with the given nodes in order
WITH path, relationships(path)[0].s as sequence
WHERE all(rel in tail(relationships(path)) WHERE rel.s = sequence)
// now each path only has relationships of common sequence
WITH path, apoc.coll.pairsMin([rel in relationships(path) | rel.p]) as pairs
WHERE all(pair in pairs WHERE pair[0] + 1 = pair[1])
RETURN path
Take the above image as an example. Using Cypher, how would I match all of the nodes except for the longest chain and the central node? I.e. all nodes within exactly one hop of the central node whilst excluding the central node (all nodes and edges except 3 nodes and 2 edges).
I have tried the following:
MATCH (n:Node) WHERE n.id = "123" MATCH path = (m)-[*1..1]->(n) RETURN m
This very nearly works, however it still returns the central node (i.e. node n). How would I exclude this node from my query result?
[UPDATED]
This will return all distinct nodes directly connected to the specified node, and explicitly prevents the specified node from being returned (in case it has a relationship to itself):
MATCH (n:Node)--(m)
WHERE n.id = "123" AND n <> m
RETURN DISTINCT m;
Ideally I would have liked to match the nodes as mentioned in my question and delete them. However, as I have not found a way to do so an inverse approach can be utilised whereby all nodes but those as mentioned in the question are matched instead. Thereby effectively excluding (but not deleting) the unwanted nodes.
This can be achieved using this query:
MATCH (n:Node) WHERE n.id = "123" MATCH path = (m)-[*2..]->(n) RETURN path
This returns the central node and all paths to that node that have a "length" greater than or equal to 2.
I am pretty new to Neo4j. I have implemented an example use case with the following setup:
acyclic directed graph
nodes have a property called externalID
Nodes:
Node Type S (Start Node)
Node Type E (End Node)
Node Type I (Intermediate Node)
Relations:
Node Type S can only have outgoing relations to Nodes of Type I
Node Type I can have ingoing relations from I and S
Node Type I can have outgoing relations to I and E
Node Type E can only have incomming relations from I
All relations have a weight property assigned which can be any number
With the help of stackoverflow and several tutorials I was able to formulate a Cypher query which gets me all paths from any start node with one externalID to the matching end node with the same externalID.
MATCH p=(a:S)-[r*]->(b:E)
WHERE a.externalID=b.externalID
WITH p, relationships(p) as rcoll
RETURN p
The query works more or less good so far ...
However, I have no idea how to change the behavior on how the graph is scanned for possible paths. Actually I only need a subset of all possible paths. Such paths fulfill the following requirement:
The path traversal is started at a Start Node S with a given capacity C.
if a relationship is traversed the weight property of this relationship is subtracted from the current capacity C (that means negative weights are added)
if the capacity gets negative the path up to this point is invalid (the path up to the previous node is still valid and may continue with other relationships)
if the capacity is still positive continue with another relationship from this point and use the result of C - weight as new C
Can I somehow adjust the query or is there any other possibility with Neo4j to get all paths using the strategy above?
Thanks a lot for your help in advance.
This Cypher query might be suitable for your use case:
MATCH p = (a:S)-[r*]->(b:E)
WHERE a.externalID = b.externalID
WITH
p,
REDUCE(c = a.capacity, r IN RELATIONSHIPS(p) |
CASE WHEN c < 0 THEN -1 ELSE c - r.weight END) AS residual
WHERE residual >= 0
RETURN p;
The REDUCE clause will set residual to a negative value if the capacity is ever reduced below 0, even if subsequent weights would normally cause it to go positive.
I have a huge database of size 260GB, which is storing a ton of transaction information. It has Agent, Customer,Phone,ID_Card as the nodes. Relationships are as follows:
Agent_Send, Customer_Send,Customer_at_Agent, Customer_used_Phone,Customer_used_ID.
A single agent is connected to many customers .And hence hitting the agent node while querying a path is not feasible. Below is my query:
match p=((ph: Phone {Phone_ID : "3851308.0"})-[r:Customer_Send
| Customer_used_ID | Customer_used_Phone *1..5]-(n2))
with nodes(p) as ns
return extract (node in ns | Labels(node) ) as Labels
I am starting with a phone number and trying to extract a big "Customer" network. I am intentionally not touching the "Customer_at_Agent" relationship in the above networked query as it is not optimal as far as performance is concerned.
So, the idea is to extract all the "Customer" labeled nodes from the path and match it with [Customer_at_Agent] relationship.
For instance , something like:
match p=((ph: Phone {Phone_ID : "3851308.0"})-[r:Customer_Send
| Customer_used_ID | Customer_used_Phone *1..5]-(n2))
with nodes(p) as ns
return extract (node in ns | Labels(node) ) as Labels
of "type customer as c "
optional match (c)-[r1:Customer_at_Agent]-(n3)
return distinct p,r1
I am still new to neo4j and cypher and I am not able to figure out a hack to extract only "customer" nodes from the path and use that in the optional match.
Thanks in advance.
Use filter notation instead of extract and you can drop any nodes that aren't labelled right. Try out this query instead:
MATCH p = (ph:Phone {Phone_ID : "3851308.0"}) - [:Customer_Send|:Customer_used_ID|:Customer_used_Phone*1..5] - ()
WITH ph, [node IN NODES(p) WHERE node:Customer] AS customer_nodes
UNWIND customer_nodes AS c_node
OPTIONAL MATCH (c_node) - [r1:Customer_at_Agent] - ()
RETURN ph, COLLECT(DISTINCT r1)
So the second line takes the phone number and the path generated and gives you a list of nodes that have the Customer label as customer_nodes. You then unwind this list so you have individual nodes you can use in path matching. Line 4 performs your optional match and finds the r1 you're interested in, then line 5 will return the phone number node you started with and a collection of all of the r1 relationships that you found on customer nodes hooked up to that phone number.
UPDATE: I added some modifications to clean up your first query line as well. If you aren't going to use an alias (like r or n2 in the first line), then don't assign them in the first place; they can affect performance and cause confusion. Empty nodes and relationships are totally fine if you don't actually have any restrictions to place on them. You also don't need parentheses to mark off a path; they are used as a core part of Cypher's ASCII art to signify nodes, so I find they are more confusing than helpful.
In a graph where the following nodes
A,B,C,D
have a relationship with each nodes successor
(A->B)
and
(B->C)
etc.
How do i make a query that starts with A and gives me all nodes (and relationships) from that and outwards.
I do not know the end node (C).
All i know is to start from A, and traverse the whole connected graph (with conditions on relationship and node type)
I think, you need to use this pattern:
(n)-[*]->(m) - variable length path of any number of relationships from n to m. (see Refcard)
A sample query would be:
MATCH path = (a:A)-[*]->()
RETURN path
Have also a look at the path functions in the refcard to expand your cypher query (I don't know what exact conditions you'll need to apply).
To get all the nodes / relationships starting at a node:
MATCH (a:A {id: "id"})-[r*]-(b)
RETURN a, r, b
This will return all the graphs originating with node A / Label A where id = "id".
One caveat - if this graph is large the query will take a long time to run.