Cypher-计算时如何遍历图形

编写查询的一种方法是

MATCH p=(A {name: 'A'})-[*1..3]-(x)
UNWIND [r IN relationships(p) | r.weight] AS weight
RETURN x.name, avg(weight) AS avgWeight
  ORDER BY avgWeight DESC
  LIMIT 1

在这里,我们将路径中的权重提取到一个列表中,然后展开该列表。试着在那里插入一个返回,看看结果在那一点上是什么样子的。因为我们可以利用 avg() avg(weight) ,同时也是最后一个路径节点的名称,聚合将按该节点名称分组。如果不想返回权重,则只返回节点名,然后更改 RETURN 到 WITH 在查询中,添加另一个只返回节点名的return子句。

您还可以添加 [n IN nodes(p) | n.name] AS nodesInPath A, B, C 等。

CREATE (A {name: 'A'}),
       (B {name: 'B'}),
       (C {name: 'C'}),
       (D {name: 'D'}),
       (E {name: 'E'}),
       (F {name: 'F'}),
(A)-[:R {weight: 2}]->(B),
(B)-[:R {weight: 4}]->(C),
(A)-[:R {weight: 3.5}]->(D),
(C)-[:R {weight: 20}]->(E),
(E)-[:R {weight: 80}]->(F)

1) 要选择长度从1到3的可能路径,请使用match with variable length relationships

MATCH p = (A)-[*1..3]->(T)

2) 然后使用 reduce function 计算平均重量。然后排序和限制以获取一个值:

MATCH p = (A)-[*1..3]->(T)
WITH p, T, 
     reduce(s=0, r in rels(p) | s + r.weight)/length(p) AS weight
RETURN T ORDER BY weight DESC LIMIT 1