我有以下数据:
<node:1><urn:connectTo><node:2>
<node:1><urn:connectTo><node:3>
<node:1><urn:connectTo><node:4>
<node:2><urn:connectTo><node:10>
<node:2><urn:connectTo><node:11>
<node:2><urn:connectTo><node:12>
<node:3><urn:connectTo><node:21>
<node:3><urn:connectTo><node:13>
<node:3><urn:connectTo><node:41>
<node:3><urn:connectTo><node:100>
<node:4><urn:connectTo><node:119>
<node:4><urn:connectTo><node:120>
如您所见,每个节点都有多个连接。我想为每个节点随机选择一个连接。我怎样才能做到这一点?我已尝试以下查询,但没有解决问题:
-
select ?currentNode ?nextNode where { ?currentNode ?p ?nextNode BIND(RAND() AS ?orderKey) } ORDER BY ?orderKey LIMIT 1
-
select ?currentNode SAMPLE(?nextNode) as ?nextNode1 where { ?currentNode ?p ?nextNode } GROUP BY ?currentNode
注意:结果给出了每个节点的第一个连接,但不是随机的
-
select ?currentNode ?nextNode (COUNT(?nextNode) AS ?noOfChoices) where { ?currentNode ?p ?nextNode BIND(RAND() AS ?orderKey) } GROUP BY ?currentNode ORDER BY ?orderKey OFFSET (RAND()*?noOfChoices) LIMIT 1
最佳答案
sample aggregate返回组内的个体:
Sample is a set function which returns an arbitrary value from the multiset passed to it. … For example, given Sample({"a", "b", "c"}), "a", "b", and "c" are all valid return values. Note that Sample() is not required to be deterministic for a given input, the only restriction is that the output value must be present in the input multiset.
这将是一个如下查询:
prefix node: <node:>
prefix urn: <urn:>
select ?source (sample(?_target) as ?target) where {
?source urn:connectTo ?_target
}
group by ?source
---------------------
| source | target |
=====================
| node:1 | node:2 |
| node:2 | node:10 |
| node:3 | node:13 |
| node:4 | node:119 |
---------------------
当然,正如您所注意到的,实现只需返回任意个体。每次都很容易相同。您可以在子查询中进行一些排序,并希望随机化目标的顺序,以便从样本获得不同的结果,但不要求结果的顺序子查询也被保留。看起来像这样:
prefix node: <node:>
prefix urn: <urn:>
select ?source (sample(?_target) as ?target) where {
{ select ?source ?_target {
?source urn:connectTo ?_target
}
order by rand() }
}
group by ?source
这似乎适用于 Apache Jena。以下是重复调用的结果:
---------------------
| source | target |
=====================
| node:1 | node:2 |
| node:2 | node:11 |
| node:3 | node:100 |
| node:4 | node:120 |
---------------------
---------------------
| source | target |
=====================
| node:1 | node:3 |
| node:2 | node:11 |
| node:3 | node:13 |
| node:4 | node:120 |
---------------------
---------------------
| source | target |
=====================
| node:1 | node:3 |
| node:2 | node:10 |
| node:3 | node:21 |
| node:4 | node:119 |
---------------------
---------------------
| source | target |
=====================
| node:1 | node:3 |
| node:2 | node:10 |
| node:3 | node:100 |
| node:4 | node:119 |
---------------------
关于random - sparql:为每个节点随机选择一个连接,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/29103024/