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scalaapache-sparkfastutil

How do I implement a fastutils map in a Spark UDAF?

I'm building a Spark UDAF where I'm storing the intermediate data in a fastutils map. Schema looks like this:

def bufferSchema = new StructType().add("my_map_col", MapType(StringType, IntegerType))

I initialize with no problem:

def initialize(buffer: MutableAggregationBuffer) = {
   buffer(0) = new Object2IntOpenHashMap[String]()
}

Problem comes when I try to update:

def update(buffer: MutableAggregationBuffer, input: Row) = { 
  val myMap = buffer.getAs[Object2IntOpenHashMap[String]](0)
  myMap.put(input.getAs[String](0), 1)
  buffer(0) = myMap
}

Getting the following error: 

Caused by: java.lang.ClassCastException: scala.collection.immutable.Map$EmptyMap$ cannot be cast to it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap

Any way I can make this work?

Solution

  • Any way I can make this work?

    Not really. This 

    buffer.getAs[Object2IntOpenHashMap[String]](0)

    is equivalent to

    buffer.get(0).asInstanceOf[Object2IntOpenHashMap[String]]]

    and the external type for MapType is scala.collection.Map.

    In practice it is a dead-end anyway - UserDefinedAggregate functions make full copy of data on each call. You might have a better luck with Aggregator (as in the linked question).