Question

我怎么能暗示对可变长度路径的限制？

我有一些start节点查询的所有可能路径：

CREATE INDEX ON :NODE(id)
MATCH all_paths_from_Start = (start:Person)-[:FRIENDSHIP*1..20]->(person:Person)
WHERE start.id = 128 AND start.country <> "Uganda"
RETURN paths;

不，我想过滤掉至少有两个人具有相同country的所有路径。 我怎么能这样做？

Answer 1

1）获取一系列国家/地区的路径，可能有重复项：REDUCE

2）删除重复项并比较数组的大小：UNWIND + COLLECT(DISTINCT...)

MATCH path = (start:Person)-[:FRIENDSHIP*1..20]->(person:Person)
      WHERE start.id = 128 AND start.country <> "Uganda"
WITH path, 
     REDUCE(acc=[], n IN NODES(path) | acc + n.country) AS countries
     UNWIND countries AS country
WITH path, 
     countries, COLLECT(DISTINCT country) AS distinctCountries
     WHERE SIZE(countries) = SIZE(distinctCountries)
RETURN path

P.S。 REDUCE可以替换为EXTRACT（感谢Gabor Szarnyas）：

MATCH path = (start:Person)-[:FRIENDSHIP*1..20]->(person:Person)
      WHERE start.id = 128 AND start.country <> "Uganda"
WITH path, 
     EXTRACT(n IN NODES(path) | n.country) AS countries
     UNWIND countries AS country
WITH path, 
     countries, COLLECT(DISTINCT country) AS distinctCountries
     WHERE SIZE(countries) = SIZE(distinctCountries)
RETURN path

P.P.S。再次感谢Gabor Szarnyas提出了另一个简化查询的想法：

MATCH path = (start:Person)-[:FRIENDSHIP*1..20]->(person:Person)
      WHERE start.id = 128 AND start.country <> "Uganda"
WITH path
     UNWIND NODES(path) AS person
WITH path, 
     COLLECT(DISTINCT person.country) as distinctCountries
     WHERE LENGTH(path) + 1 = SIZE(distinctCountries)
RETURN path

Answer 2

我能想到的一个解决方案是获取路径的nodes，以及路径中每个人extract来自同一国家/地区的人数（我们通过filter确定同一个国家/地区。如果来自同一个国家/地区的人数为零，则路径中包含来自独特国家/地区的人员，即对于所有人员，只有一个人（他/她自己）来自该国家/地区。国家。

MATCH p = (start:Person {id: 128})-[:FRIENDSHIP*1..20]->(person:Person)
WHERE start.country <> "Uganda"
WITH p, nodes(p) AS persons
WITH p, extract(p1 IN persons | size(filter(p2 IN persons WHERE p1.country = p2.country))) AS personsFromSameCountry
WHERE length(filter(p3 IN personsFromSameCountry WHERE p3 > 1)) = 0
RETURN p

查询在语法上是正确的，但我没有对任何数据进行测试。

请注意，我已将id = 128条件移至模式，并将all_paths_from_Start变量缩短为p。

Neo4J Cypher：按标准过滤掉可变长度路径

2 个答案: