Question

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？我尝试了以下查询，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

Answer 1

sample aggregate会从群组中返回个人：

Sample是一个set函数，它从中返回一个任意值 multiset传递给它。 ...例如，给定样本（{＆＃34; a＆＃34;，＆＃34; b＆＃34;，＆＃34; c＆＃34;}），＆＃34; a＆＃34;，＆＃34; b＆＃34;，＆＃34; c＆＃34;都是有效的返回值。注意对于给定的输入，Sample（）不需要是确定性的唯一的限制是输出中必须存在输出值多重集。

这将是一个类似的查询：

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，正如您所指出的，实现只需要返回任意个体。这很容易就是每次相同的。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，以便从示例获得不同的结果，但是并不要求子查询的结果顺序也被保留。这看起来像这样：

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 |
---------------------

sparql：为每个节点随机选择一个连接

1 个答案: