[英]Cypher query: Assigning an aggregate value as a property of a relationship
根据这个问题 ,我有以下玩具示例:
CREATE (A1:Worker {ref:"A1"})
CREATE (A2:Worker {ref:"A2"})
CREATE (B1:Worker {ref:"B1"})
CREATE (B2:Worker {ref:"B2"})
CREATE (A1)-[:StreamsTo {type:"stream1"}]->(B1)
CREATE (A1)-[:StreamsTo {type:"stream2"}]->(B1)
CREATE (A1)-[:StreamsTo {type:"stream3"}]->(B1)
CREATE (A1)-[:StreamsTo {type:"stream1"}]->(B2)
CREATE (A1)-[:StreamsTo {type:"stream2"}]->(B2)
CREATE (A2)-[:StreamsTo {type:"stream1"}]->(B1)
CREATE (A2)-[:StreamsTo {type:"stream1"}]->(B2)
CREATE (A2)-[:StreamsTo {type:"stream2"}]->(B2);
这将产生以下图形:
我想做的是计算离开源节点的每种流类型的路由概率(RP),该概率为1 /该类型的传出关系的数量。 我可以使用以下查询计算RP值:
MATCH (source:Worker)-[st:StreamsTo]->(:Worker)
RETURN source.ref as Worker,
st.type as StreamType,
COUNT(st) as OutgoingCount,
1.0 / COUNT(st) as RP
ORDER BY source.ref, st.type;
结果是:
╒════════╤════════════╤═══════════════╤════╕
│"Worker"│"StreamType"│"OutgoingCount"│"RP"│
╞════════╪════════════╪═══════════════╪════╡
│"A1" │"stream1" │2 │0.5 │
├────────┼────────────┼───────────────┼────┤
│"A1" │"stream2" │2 │0.5 │
├────────┼────────────┼───────────────┼────┤
│"A1" │"stream3" │1 │1 │
├────────┼────────────┼───────────────┼────┤
│"A2" │"stream1" │2 │0.5 │
├────────┼────────────┼───────────────┼────┤
│"A2" │"stream2" │1 │1 │
└────────┴────────────┴───────────────┴────┘
因此,我现在需要做的是获取每个源节点(Worker)和流类型组合的计算出的RP值,并将该值添加为离开给定源节点的该类型的每个关系的属性。
我知道我可以使用WITH
将上面查询的输出传递给新查询。 但是,我坚持如何将总RP值应用于来自具有给定属性的给定源的所有关系? 我已经知道在cypher中可以将结果收集到地图中,但是我不确定如何在查询中使用它?
我可以在应用程序端执行此操作,但是如果可能的话,显然希望在服务器端执行此操作。
MATCH (source:Worker)-[st:StreamsTo]->(:Worker)
// do the calculations, collection st relations into sts array
WITH collect(st) as sts, source.ref as Worker,
st.type as StreamType,
COUNT(st) as OutgoingCount,
1.0 / COUNT(st) as RP
// expanding sts list to st rows
UNWIND sts as st
// set the property sr.RP = RP
set st.RP = RP
// collect st again to avoid a cartesian product
WITH collect(st) as sts, Worker, StreamType, OutgoingCount, RP
// return desired data, ordering
return Worker, StreamType, OutgoingCount, RP
ORDER BY Worker, StreamType
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