How to iterate a cypher query multiple time

[spsingh559]

Hi Team,

I have a cypher query which is basically an algorithm which i need to iterate multiple times in order to get the final result. It's same like how we set iteration options in GDS libraries.

I have tried using foreach with range and it throws an error " Invalid use of match inside foreach". What could be the possible ways to add for loop like functionality in graph?

[Cobra]

Hello @spsingh559

Can you show us some code?

Regards,
Cobra

[spsingh559]

sure, here is one algorithm we have created for risk propagation among Person node based on their interaction with each other.

with 0.8 as Decay, 20 as itr

match (p:Person)-[r:MET_EVENT]->(a:Person) where r.timeEnd>Datetime()-Duration('P14D')
with toFloat(SUM(a.riskScore))/toFloat(count(a)) * Decay as score,p

FOREACH ( ignoreMe in CASE WHEN p.riskScore<score THEN [1] ELSE END | set p.riskScore=score )
return SUM(p.riskScore) as totalRiskScore

Note : this query i need to run more than 20 + time till there is convergence . My aim is to iterate the query till totalRiskScore is converged to a point, when there is no further change in score. That can be achieved by iterating this query over 20 - 25 times. Now how i would iterate this query multiple times.

[Cobra]

Did you to use UNWIND for your iteration?

Regards,
Cobra

[spsingh559]

yes, i have tried with unwind too, but in case of unwind, query is iterative over a given range, but value of result is not getting changes.

See the code snippet with unwind -

UNWIND range(0,10) as iterations
with 0.8 as Decay, 20 as itr, iterations

match (p:Person)-[r:MET_EVENT]->(a:Person) where r.timeEnd>Datetime()-Duration('P14D')
with toFloat(SUM(a.riskScore))/toFloat(count(a)) * Decay as score,p, iterations

FOREACH ( ignoreMe in CASE WHEN p.riskScore<score THEN [1] ELSE END | set p.riskScore=score )
return SUM(p.riskScore) as totalRiskScore,iterations

Result :

Now you can notice that risk score is remain same for each iteration, but ideal behaviour is risk score will keep on changing over each iteration .

[Cobra · Accepted solution]

Yeah, you right

Maybe UNWIND + your cypher request in apoc.cypher.run() doc

Regards,
Cobra

[spsingh559]

finally i found the way using your shared document. I am using apoc.cypher.doIt -> as i am modifying records also. Run is for only reading the records.

Upadted snippet is

UNWIND range(0,100) as iterations

call apoc.cypher.doIt("
with 0.8 as Decay, 20 as itr
match (p:Person)-[r:MET_EVENT]->(a:Person) where r.timeEnd>Datetime()-Duration('P14D')
with toFloat(SUM(a.riskScore))/toFloat(count(a)) * Decay as score,p

FOREACH ( ignoreMe in CASE WHEN p.riskScore<score THEN [1] ELSE END | set p.riskScore=score )
return SUM(p.riskScore) as totalRiskScore
",{}) yield value

return value

Now value is changing over each iteration

[Cobra]

Nice, I'm happy to hear it, good job