Structured steaming groupBy agg collect_list Collect cannot be used in partial aggregations

问题

stateDF
.withWatermark("t","1 seconds")
.groupBy(window($"t","1 minutes","1 minutes"),$"hid")
.agg(collect_list("id"))
.writeStream.outputMode("append")
.format("console").trigger(ProcessingTime("1 minutes"))
.start().awaitTermination()

When I add 'collect_list', I'll have this problem. But by spark core it can be done. ERROR：

java.lang.RuntimeException: Collect cannot be used in partial aggregations. at scala.sys.package$.error(package.scala:27) at ...

java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748) enter code here

回答1:

Through my exploration,I have two solutions to this problem.

Methed 1:Modifying the source code with SPARK-1893,But I don't recommend doing this.

Methed 2:Making user-defined aggregate functions (UDAF) for yourself.Although this is troublesome, it is effective.The following is my code, welcome correct!

class CollectList extends UserDefinedAggregateFunction {

  override def inputSchema: StructType = StructType(StructField("id", StringType, nullable = true) :: StructField("state", StringType, nullable = true):: Nil)

  override def bufferSchema: StructType = StructType(StructField("ids", ArrayType(StringType, containsNull = true), nullable = true) :: Nil)

  override def dataType: ArrayType = ArrayType(StringType, containsNull = true)

  override def deterministic: Boolean = false

  override def initialize(buffer: MutableAggregationBuffer): Unit = {
    buffer(0) = null
  }

  override def update(buffer: MutableAggregationBuffer, input: Row): Unit = {
    if (buffer.get(0) == null){
      buffer(0) = Array(input.getString(0) + "_" + input.getString(1))
    }
    else {
      val s = input.getString(0) + "_" + input.getString(1)
      val b = buffer.getAs[Seq[String]](0)
      buffer(0) = b :+ s
    }

  }

  override def merge(buffer1: MutableAggregationBuffer, buffer2: Row): Unit = {
    if (buffer1.getAs[Seq[String]](0) == null){
      buffer1(0) = buffer2.getAs[Seq[String]](0).distinct
    }
    else {
      buffer1(0) = (buffer1.getAs[Seq[String]](0) ++ buffer2.getAs[Seq[String]](0)).distinct
    }
  }

  override def evaluate(buffer: Row): Any = buffer.getAs[Seq[String]](0)

}

来源：https://stackoverflow.com/questions/50459006/structured-steaming-groupby-agg-collect-list-collect-cannot-be-used-in-partial-a

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