How can neo4j query all nodes that are 3 away from a node in a digraph

Refer to GPT and your own ideas, you can use Cypher language to query all nodes in the Neo4j graph database that are 3 away from a node and their paths. Here is a possible query:

MATCH path=(startNode)-[*3]-(endNode)
WHERE startNode.id = 1
RETURN path

This query uses the MATCH clause to find all paths that meet the criteria, where startNode is the start node, endNode is the destination node, and [*3] represents all nodes in the path that are 3 away from the start node. The WHERE clause restricts the id of the start node to 1.

If you only want to RETURN all nodes and the paths between them, you can use the return clause of the MATCH clause to specify which nodes and paths to return, as follows:

MATCH path=(startNode)-[*3]-(endNode)
WHERE startNode.id = 1
RETURN [node in nodes(path) | node.id] AS nodes, 
       reduce(acc="", rel in relationships(path) | acc + "->" + type(rel)) AS path

This query uses the nodes(path) function to extract all nodes in the path and then convert their ids into a list using list comprehensions. Use the reduce() function to extract all the relationships in the path and concatenate them using the string concatenation operator +. Finally, two lists are returned: nodes and path, where nodes contains the ids of all nodes, and path is the path between nodes.

Here it is assumed that the node has an attribute id, which you need to replace with the actual attribute name.
Here is a simple example:

Suppose we have the following digraph:

(A) --> (B) --> (C) --> (D) --> (E) --> (F)
 ^                                       |
  \--------------------------------------/

We want to query all nodes that are 3 away from node A and the paths between them.

You can use the following code:

MATCH (a:Node {name: 'A'})-[:CONNECTED_TO*3]-(d)
RETURN d.name, 
       reduce(path = '', r in relationships(p) | path + '->' + endNode(r).name)[1..] AS path

In this query, we use the MATCH clause to specify that the starting node is A node named "A", and we use the relationship type "CONNECTED_TO" and the relationship path length "*" to specify that we want to query a node that is 3 away from this node. We store the result in variable d.

Then, we return the name of d, and the path to which the reduce function evaluates. The reduce function concatenates the terminating nodes of each relationship in the path, using the arrow symbol "->" Separate. This creates an array of strings where the first element is the path string(excluding the start node).

Finally, we leave the first element of the path string, that is, we cut from the second element, because we don't need to include the start node.

The output of this query should be:

╒════════╤═══════════════╕
│"d.name"│"path"         │
╞════════╪═══════════════╡
│"D"     │"B->C->D"      │
├────────┼───────────────┤
│"F"     │"E->F"         │
└────────┴───────────────┘

refers to nodes D and F, and the path between them.
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The following answers are based on ChatGPT and GISer Liu:

To query all nodes in a digraph that are 3 away from a node, Cypher query language is used.

Suppose we want to query all nodes that are 3 away from node 1, we can use the following query:

MATCH (n1)-[*3]-(n2)
WHERE n1.id = 1 AND n1 <> n2
RETURN DISTINCT n2, [n IN nodes(path) | n.id] as path

The above query uses the MATCH statement to match all nodes that are 3 away from node 1. WHERE, [*3] indicates that the path length is 3, and(n1) and(n2) are the starting point and ending point, while the WHERE statement is used to restrict the starting point to node 1 and exclude cases where the path contains the starting point. Finally, use a RETURN statement to return all eligible nodes and the paths between them. In the path, we use the nodes(path) function to get all nodes on the path, and we use list comprehension to generate a list of format id.

To avoid duplicate nodes in the result path, we use the DISTINCT keyword to filter out duplicate results.

This answer quotes ChatGPT

You can query and return the paths between all nodes using the Cypher query language and represent them in the format "1-> 2-> 3-> A string of 4". Assuming you know the starting node is "1", you can use the following query statement:

MATCH path = (startNode)-[*]-(endNode)
WHERE startNode.id = '1'
RETURN reduce(pathString = '', n in nodes(path) | pathString + (case when pathString='' then '' else '->' end) + n.id) AS pathString

The above query returns the paths from node "1" through all possible paths to the node. Each path is represented as a string marked by the arrow symbol "->" id of the separated node.

Specifically, MATCH path =(startNode)-[ ]-(endNode) looks for all paths starting at "1", where -[ ]- indicates any length of relationship chain, WHERE startNode.id = '1' is used to specify the start node. The reduce function concatenates the ids of all nodes in the path into a string, where(case when pathString= "then" 'else '-> 'end) is used to add an arrow symbol before the id of each node, and n..i is used to get the id of the current node. The final return is a string variable named "pathString" that represents the full path from node "1" to each node in the path.

Note that if there is a loop in the graph, then the query may enter an endless loop, as it tries to keep progressing through the loop. To avoid this, use LIMIT to limit the maximum length of the path.

Based on Monster group and GPT write:
Use Cypher query language to query all nodes in a digraph that are 3 away from a node and the paths between them. Here is a sample query:

MATCH path = (start:Node {id: 1})-[:LINK*3]->(end:Node)
RETURN [n IN nodes(path) | n.id] as nodes, reduce(output = "", rel in relationships(path) | output + rel.start_node.id + "->" + rel.end_node.id + "->") + end.id as path

In the above query, Node is the node label, id is the attribute of the node, LINK is the side label, and *3 indicates that the length of the path is 3.

query result returns a table with two columns. The first column is the ID of all the nodes and the second column is the path between the nodes. The format is 1-> 2-> 3-> 4. If the path contains multiple nodes, they are marked with arrows -> Connect. If there is only one node in the path, the path is empty.