如何在Scala中使用Spark RDD删除重复项(更多为基于多个属性的过滤器)? [英] How to remove duplicates (more like filter based on multiple properties) with Spark RDD in Scala?
问题描述
作为一项政策,我们不更新我们的文档,但是我们使用更新的值重新创建。当我处理这些事件时,我只想保留更新的内容,所以我想根据多个值过滤RDD中的项目。例如,说一个项目是:
As a policy, we do not update our documents, but we recreate with updated values. When I will process the events, I would like to keep only the updated ones, so I would like to filter items out of my RDD based on multiple values. For instance, say an item would be:
{
"name": "Sample",
"someId": "123",
"createdAt": "2016-09-21T02:16:32+00:00"
}
,何时更新:
{
"name": "Sample-Updated",
"someId": "123", # This remains the same
"createdAt": "2016-09-21T03:16:32+00:00" # This is greater than the one of above, since the update operation is done after the document is generated
}
我一直在做的是:
items = items.toList.
.sortBy(_.createdAt).reverse
items = items
.groupBy(_.someId)
.map(_._2.head)(breakOut)
但这显然将RDD转换为列表;火花结束如何实现?
but this obviously converts RDD into a list; end of Spark. How do I achieve this?
更新
到目前为止,这是通过查看评论,但没有运气添加到集合:
So far, I have achieved this by looking into comments, but no luck when adding into set:
// Is this correct? (1)
val initialSet = sc.parallelize(List[(String, Event)]())
val addToSet = (eventSet: RDD[(String, Event)],
event: Event) => {
// What to do here? (2)
}
// Is this correct? (3)
val mergeSets = (p1: RDD[(String, Event)],
p2: RDD[(String, Event)]) => p1.union(p2)
// resultSet is of type RDD[(String, RDD[(String, Event)])]. How to get it as RDD[(String, Event)]? (4)
val resultSet = initialSet.aggregateByKey(initialSet)(addToSet, mergeSets)
推荐答案
你应该可以在这里使用 reduceByKey
You should be able to use reduceByKey
here:
rdd
.keyBy(_.someId)
.reduceByKey((x, y) => if (x.createdAt > y.createdAt) x else y)
.values
其中初始 keyBy
创建(id,object)
, reduceByKey
选择最近的对象,值
drop keys。
where initial keyBy
creates (id, object)
, reduceByKey
selects the most recent object, and values
drops keys.
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