Expand paths

The expand paths procedure is the most basic of the path expanders. This procedure enables path traversals based on relationship filters and node filters. See Expand paths with config if more control is required over the traversal.

Procedure Overview

The procedure is described below:

Qualified Name Type

apoc.path.expand

apoc.path.expand(startNode <id>|Node|list, 'TYPE|TYPE_OUT>|<TYPE_IN', '+YesLabel|-NoLabel', minLevel, maxLevel ) yield path - expand from start node following the given relationships from min to max-level adhering to the label filters

Procedure

Parameter Syntax

This procedure takes the following parameters:

  • start - a list of nodes or node ids

  • relationshipFilter - the relationship types to be expanded

  • labelFilter - the node labels to be expanded

  • minLevel - the minimum number of hops in our traversal

  • maxLevel - the maximum number of hops in our traversal

Relationship Filters

The syntax for relationship filters is described below:

Syntax: [<]RELATIONSHIP_TYPE1[>]|[<]RELATIONSHIP_TYPE2[>]|…​

input type direction

LIKES>

LIKES

OUTGOING

<FOLLOWS

FOLLOWS

INCOMING

KNOWS

KNOWS

BOTH

>

any type

OUTGOING

<

any type

INCOMING

Label Filters

The syntax for label filters is described below:

Syntax: [+-/>]LABEL1|LABEL2|*|…​

input result

-Foe

blacklist filter - No node in the path will have a label in the blacklist.

+Friend

whitelist filter - All nodes in the path must have a label in the whitelist (exempting termination and end nodes, if using those filters). If no whitelist operator is present, all labels are considered whitelisted.

/Friend

termination filter - Only return paths up to a node of the given labels, and stop further expansion beyond it. Termination nodes do not have to respect the whitelist. Termination filtering takes precedence over end node filtering.

>Friend

end node filter - Only return paths up to a node of the given labels, but continue expansion to match on end nodes beyond it. End nodes do not have to respect the whitelist to be returned, but expansion beyond them is only allowed if the node has a label in the whitelist.

Examples

The examples in this section are based on the following sample graph:

MERGE (mark:Person:DevRel {name: "Mark"})
MERGE (praveena:Person:Engineering {name: "Praveena"})
MERGE (joe:Person:Field {name: "Joe"})
MERGE (lju:Person:DevRel {name: "Lju"})
MERGE (zhen:Person:Engineering {name: "Zhen"})
MERGE (stefan:Person:Field {name: "Stefan"})
MERGE (alicia:Person:Product {name: "Alicia"})
MERGE (martin:Person:Engineering {name: "Martin"})
MERGE (jake:Person:Product {name: "Jake"})

MERGE (zhen)-[:KNOWS]-(stefan)
MERGE (zhen)-[:KNOWS]-(lju)
MERGE (zhen)-[:KNOWS]-(praveena)
MERGE (zhen)-[:KNOWS]-(martin)
MERGE (mark)-[:KNOWS]-(jake)
MERGE (alicia)-[:KNOWS]-(jake)

MERGE (alicia)-[:FOLLOWS]->(joe)
MERGE (joe)-[:FOLLOWS]->(mark)
MERGE (joe)-[:FOLLOWS]->(praveena)
MERGE (joe)-[:FOLLOWS]->(zhen)
MERGE (mark)-[:FOLLOWS]->(stefan)
MERGE (stefan)-[:FOLLOWS]->(joe)
MERGE (praveena)-[:FOLLOWS]->(joe)

The Neo4j Browser visualization below shows the sample graph:

apoc.path.expand

The KNOWS relationship type is considered to be bidirectional, where if Zhen knows Stefan, we can imply that Stefan knows Zhen. When using the KNOWS relationship we will ignore the direction.

The FOLLOWS relationship has a direction, so we will specify a direction when we use it.

Let’s start by expanding paths from the Praveena node. We only want to consider the KNOWS relationship type, so we’ll specify that as the relationship filter.

The following returns the paths to people that Praveena KNOWS from 1 to 2 hops
MATCH (p:Person {name: "Praveena"})
CALL apoc.path.expand(p, "KNOWS", null, 1, 2)
YIELD path
RETURN path, length(path) AS hops
ORDER BY hops;
Table 1. Results
path hops

(:Person:Engineering {name: "Praveena"})←[:KNOWS]-(:Person:Engineering {name: "Zhen"})

1

(:Person:Engineering {name: "Praveena"})←[:KNOWS]-(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:Engineering {name: "Martin"})

2

(:Person:Engineering {name: "Praveena"})←[:KNOWS]-(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:DevRel {name: "Lju"})

2

(:Person:Engineering {name: "Praveena"})←[:KNOWS]-(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:Field {name: "Stefan"})

2

Praveena only has a direct KNOWS relationship to Zhen, but Zhen has KNOWS relationships to 3 other people, which means they’re 2 hops away from Praveena.

We can also provide a node label filter to restrict the nodes that are returned. The following query only returns paths where every node has the Engineering label.

The following returns paths containing only Engineering people that Praveena KNOWS from 1 to 2 hops
MATCH (p:Person {name: "Praveena"})
CALL apoc.path.expand(p, "KNOWS", "+Engineering", 1, 2)
YIELD path
RETURN path, length(path) AS hops
ORDER BY hops;
Table 2. Results
path hops

(:Person:Engineering {name: "Praveena"})←[:KNOWS]-(:Person:Engineering {name: "Zhen"})

1

(:Person:Engineering {name: "Praveena"})←[:KNOWS]-(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:Engineering {name: "Martin"})

2

We lose the paths that ended with Lju and Stefan because neither of those nodes had the Engineering label.

We can specify multiple relationship types. The following query starts from the Alicia node, and then expands the FOLLOWS and KNOWS relationships:

The following returns paths containing people that Alicia FOLLOWS or KNOWS from 1 to 3 hops
MATCH (p:Person {name: "Alicia"})
CALL apoc.path.expand(p, "FOLLOWS>|KNOWS", "", 1, 3)
YIELD path
RETURN path, length(path) AS hops
ORDER BY hops;
Table 3. Results
path hops

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})

1

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Sales {name: "Jonny"})

1

(:Person:Product {name: "Alicia"})-[:KNOWS]→(:Person:Product {name: "Jake"})

1

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})

2

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Praveena"})

2

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:DevRel {name: "Mark"})

2

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Sales {name: "Jonny"})-[:KNOWS]→(:Person:Sales {name: "Anthony"})

2

(:Person:Product {name: "Alicia"})-[:KNOWS]→(:Person:Product {name: "Jake"})←[:KNOWS]-(:Person:DevRel {name: "Mark"})

2

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})-[:FOLLOWS]→(:Person:Product {name: "John"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:Engineering {name: "Martin"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:Engineering {name: "Praveena"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:DevRel {name: "Lju"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:Field {name: "Stefan"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Praveena"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Praveena"})←[:KNOWS]-(:Person:Engineering {name: "Zhen"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:DevRel {name: "Mark"})-[:FOLLOWS]→(:Person:Field {name: "Stefan"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:DevRel {name: "Mark"})-[:KNOWS]→(:Person:Product {name: "Jake"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Sales {name: "Jonny"})-[:KNOWS]→(:Person:Sales {name: "Anthony"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})

3

(:Person:Product {name: "Alicia"})-[:KNOWS]→(:Person:Product {name: "Jake"})←[:KNOWS]-(:Person:DevRel {name: "Mark"})-[:FOLLOWS]→(:Person:Field {name: "Stefan"})

3

This query returns 19 paths, Alicia is very well connected!

We can also specify traversal termination criteria using label filters. If we wanted to terminate a traversal as soon as the traversal encounters a node containing the Engineering label, we can use the /Engineering node filter.

The following returns paths containing people that Alicia FOLLOWS or KNOWS from 1 to 3 hops, terminating as soon as a node with the Engineering label is reached
MATCH (p:Person {name: "Alicia"})
CALL apoc.path.expand(p, "FOLLOWS>|KNOWS", "/Engineering", 1, 3)
YIELD path
RETURN path, length(path) AS hops
ORDER BY hops;
Table 4. Results
path hops

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})

2

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Praveena"})

2

We’re now down to only two paths. But this query doesn’t capture all of the paths from Alicia that end in a node with the Engineering label. We can use the >Engineering node filter to define a traversal that:

  • only returns paths that terminate at nodes with the Engineering label

  • continues expansion to end nodes after that, looking for more paths that end with the Engineering label

The following returns paths containing people that Alicia FOLLOWS or KNOWS from 1 to 3 hops, where paths end with a node with the Engineering label
MATCH (p:Person {name: "Alicia"})
CALL apoc.path.expand(p, "FOLLOWS>|KNOWS", ">Engineering", 1, 3)
YIELD path
RETURN path, length(path) AS hops
ORDER BY hops;
Table 5. Results
path hops

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})

2

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Praveena"})

2

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:Engineering {name: "Martin"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Zhen"})-[:KNOWS]→(:Person:Engineering {name: "Praveena"})

3

(:Person:Product {name: "Alicia"})-[:FOLLOWS]→(:Person:Field {name: "Joe"})-[:FOLLOWS]→(:Person:Engineering {name: "Praveena"})←[:KNOWS]-(:Person:Engineering {name: "Zhen"})

3

Our query now also returns paths going through Praveena and Zhen, one going to Martin, and other others going back to Zhen and Praveena!