cloud-fan commented on a change in pull request #23304: [SPARK-26353][SQL]Add
typed aggregate functions(max/min) to the example module.
URL: https://github.com/apache/spark/pull/23304#discussion_r257271503
##########
File path:
examples/src/main/scala/org/apache/spark/examples/sql/SimpleTypedAggregator.scala
##########
@@ -84,3 +91,71 @@ class TypedAverage[IN](val f: IN => Double) extends
Aggregator[IN, (Double, Long
}
override def outputEncoder: Encoder[Double] = Encoders.scalaDouble
}
+
+class TypedMin[IN](val f: IN => Double) extends Aggregator[IN, MutableDouble,
Option[Double]] {
+ override def zero: MutableDouble = null
+ override def reduce(b: MutableDouble, a: IN): MutableDouble = {
+ if (b == null) {
+ new MutableDouble(f(a))
+ } else {
+ b.value = math.min(b.value, f(a))
+ b
+ }
+ }
+ override def merge(b1: MutableDouble, b2: MutableDouble): MutableDouble = {
+ if (b1 == null) {
+ b2
+ } else if (b2 == null) {
+ b1
+ } else {
+ b1.value = math.min(b1.value, b2.value)
+ b1
+ }
+ }
+ override def finish(reduction: MutableDouble): Option[Double] = {
+ if (reduction != null) {
+ Some(reduction.value)
+ } else {
+ None
+ }
+ }
+
+ override def bufferEncoder: Encoder[MutableDouble] =
Encoders.kryo[MutableDouble]
+ override def outputEncoder: Encoder[Option[Double]] =
ExpressionEncoder[Option[Double]]()
Review comment:
can we use `Encoders.product[Option[Double]]`? Or we can use
`Encoders.DOUBLE` and use null to represent `None`.
The thing is, `ExpressionEncoder` is an internal class and we should avoid
exposing it in the example module.
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