如何在节点之间创建随机关系？

Question

I'm trying to create random transaction between bank accounts. I have created the following query:

//Create transactions
CALL apoc.periodic.iterate("
match (a:BANK_ACCOUNT)
WITH apoc.coll.randomItem(collect(a)) as sender
return sender", "
MATCH (b:BANK_ACCOUNT)
WHERE NOT sender = b
WITH apoc.coll.randomItem(collect(b)) as receiver
MERGE (sender)-[r:HAS_TRANSFERED {time: datetime()}]->(receiver)
set r.amount = rand()*1000",
{batchSize:100, parallel:false});

I would assume that it would create 100 random transactions between random bank accounts. Instead it creates 1 new bank account and 1 new relationship. What am I doing wrong and what should I do?

Thanks for your help !

Answer 1

The following query uses apoc.coll.randomItems to get 200 different random accounts at one time (which is much faster than getting one random account 200 times):

MATCH (ba:BankAccount)
WITH apoc.coll.randomItems(COLLECT(ba), 200) AS accts
WHERE SIZE(accts) > 1 
UNWIND RANGE(0, SIZE(accts)/2*2-1, 2) AS i
WITH accts[i] AS sender, accts[i+1] AS receiver
CREATE (sender)-[:TRANSFERED_TO {time: datetime()}]->(receiver)

Notes:

1. This query uses CREATE instead of MERGE because it is unlikely that a TRANSFERED_TO relationship already exists with the current time as the time value. (You can choose to use MERGE anyway, if duplication is still possible.)
2. The WHERE SIZE(accts) > 1 test avoids errors when there are not at least 2 accounts.
3. SIZE(accts)/2*2-1 calculation prevents the RANGE function from generating a list index ( i ) that exceeds the last valid index for a sender account.