Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/10960#discussion_r51533782
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/Covariance.scala
---
@@ -28,171 +26,90 @@ import org.apache.spark.sql.types._
* When applied on empty data (i.e., count is zero), it returns NULL.
*
*/
-abstract class Covariance(left: Expression, right: Expression) extends
ImperativeAggregate
- with Serializable {
- override def children: Seq[Expression] = Seq(left, right)
+abstract class Covariance(x: Expression, y: Expression) extends
DeclarativeAggregate {
+ override def children: Seq[Expression] = Seq(x, y)
override def nullable: Boolean = true
-
override def dataType: DataType = DoubleType
-
override def inputTypes: Seq[AbstractDataType] = Seq(DoubleType,
DoubleType)
- override def checkInputDataTypes(): TypeCheckResult = {
- if (left.dataType.isInstanceOf[DoubleType] &&
right.dataType.isInstanceOf[DoubleType]) {
- TypeCheckResult.TypeCheckSuccess
+ protected val count = AttributeReference("count", DoubleType, nullable =
false)()
+ protected val xAvg = AttributeReference("xAvg", DoubleType, nullable =
false)()
+ protected val yAvg = AttributeReference("yAvg", DoubleType, nullable =
false)()
+ protected val ck = AttributeReference("ck", DoubleType, nullable =
false)()
+
+ override val aggBufferAttributes: Seq[AttributeReference] = Seq(count,
xAvg, yAvg, ck)
+
+ override val initialValues: Seq[Expression] = Seq(
+ /* count = */ Literal(0.0),
+ /* xAvg = */ Literal(0.0),
+ /* yAvg = */ Literal(0.0),
+ /* ck = */ Literal(0.0)
+ )
+
+ override lazy val updateExpressions: Seq[Expression] = {
+ val n = count + Literal(1.0)
+ val dx = x - xAvg
+ val dy = y - yAvg
+ val dyN = dy / n
+ val newXAvg = xAvg + dx / n
+ val newYAvg = yAvg + dyN
+ val newCk = ck + dx * (dy - dyN)
+
+ val isNull = Or(IsNull(x), IsNull(y))
--- End diff --
Ditto.
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