Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/18113#discussion_r154889195
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/typedaggregators.scala
---
@@ -99,3 +96,165 @@ class TypedAverage[IN](val f: IN => Double) extends
Aggregator[IN, (Double, Long
toColumn.asInstanceOf[TypedColumn[IN, java.lang.Double]]
}
}
+
+class TypedMinDouble[IN](val f: IN => Double)
+ extends Aggregator[IN, MutableDouble, java.lang.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): java.lang.Double = {
+ if (reduction == null) {
+ null
+ } else {
+ reduction.toJavaDouble
+ }
+ }
+
+ override def bufferEncoder: Encoder[MutableDouble] =
Encoders.kryo[MutableDouble]
+ override def outputEncoder: Encoder[java.lang.Double] =
ExpressionEncoder[java.lang.Double]()
+
+ // Java api support
+ def this(f: MapFunction[IN, java.lang.Double]) = this((x: IN) =>
f.call(x))
+ def toColumnScala: TypedColumn[IN, Double] = {
--- End diff --
seems it's hard to achieve, how about
```
trait TypedMinDouble[IN, OUT](val f: IN => Double) extends Aggregator[IN,
MutableDouble, OUT] {
def zero = ...
def reduce = ...
}
class JavaTypedMinDouble[IN](val f: IN => Double) extend TypedMinDouble[IN,
JDouble](f) {
def finish: JDouble
}
class ScalaTypedMinDouble[IN](val f: IN => Double) extends
TypedMinDouble[IN, Option[Double](f) {
def finish: Option[Double]
}
```
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