Cut off unnecessary relationships

[Percedal]

Hello! I have graphs consisting of student nodes and classmate relationships (s1)-[:classmate]->(s2).
Is it possible to write a query that cuts off relations between fake classmates? For example, here it is necessary to cut off the Donskoy Ilya.

[david_allen]

Depends on which relationships are fake, but deleting relationships is easy, and done like this:

MATCH (:Person { name: "A" })-[rel:classmate]->(:Person { name: "B" })
DELETE rel
RETURN true;

Now all you have to do is adjust the MATCH to catch the fake ones, and it'll be taken care of.

[Percedal]

In fact, the task is difficult. Relationships are considered fake when a student is a classmate of only one student from a group of classmates.

[krisgeus]

david.allen:

MATCH (:Person { name: "A" })-[rel:classmate]->(:Person { name: "B" }) DELETE rel RETURN true;

something like this might work. Not tested so not sure it is corrrect syntax wise or if you need less then or equal in the where clause

MATCH (a:Person { name: "A" })-[rel:classmate]->(b:Person { name: "B" })
WITH size((b)-[:classmate]->() ) AS others_classmates, 
     size((a)-[:classmate]->() ) AS own_classmates,
WHERE own_classmates < others_classmates
DELETE rel
RETURN true;

[Percedal]

I tried:
MATCH (a:student)-[rel:classmate]->(b:student)
WITH size((b)-[:classmate]->() ) AS others_classmates,
size((a)-[:classmate]->() ) AS own_classmates,
WHERE own_classmates < others_classmates
DELETE rel
RETURN true;

Error:
Neo.ClientError.Statement.SyntaxError
Invalid input 'w': expected 'r/R' or 'p/P' (line 4, column 8 (offset: 162))
"WHERE own_classmates < others_classmates"
^

[moritzlukasscha]

You inserted a comma before your WHERE statement.
If you remove it, it should work.

So it should be like:

MATCH (a:student)-[rel:classmate]->(b:student)
WITH size((b)-[:classmate]->() ) AS others_classmates,
size((a)-[:classmate]->() ) AS own_classmates
WHERE own_classmates < others_classmates
DELETE rel
RETURN true;

[krisgeus]

Yes indeed. Typo on my side. Thanks for noticing @moritzlukasschauer

[Percedal]

Hi. I have an error: Variable rel not defined (line 5, column 8 (offset: 196))
"DELETE rel".

[moritzlukasscha]

Hey,

the variable is defined in the MATCH-clause, but not in the WITH-clause.

So something like

WITH size((b)-[:classmate]->() ) AS others_classmates,
     size((a)-[:classmate]->() ) AS own_classmates,
     rel

should work for you.

[Percedal]

This code seems to have helped me.

MATCH (a:student)-[rel:classmate]->(b:student)
WITH size((b)-[:classmate]->() ) AS others_classmates,
size((a)-[:classmate]->() ) AS own_classmates, a, b, rel
WHERE others_classmates >= own_classmates
DELETE rel

[mdfrenchman]

Be careful using size though. You could get a fake classmate counting as valid if they have the same number of classmates, but not necessarily the exact same classmates.

You would probably want to compare classmate collections for that.

-Mike