Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/10960#discussion_r51547587
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/CentralMomentAgg.scala
---
@@ -52,178 +50,162 @@ abstract class CentralMomentAgg(child: Expression)
extends ImperativeAggregate w
protected def momentOrder: Int
override def children: Seq[Expression] = Seq(child)
-
override def nullable: Boolean = true
-
override def dataType: DataType = DoubleType
+ override def inputTypes: Seq[AbstractDataType] = Seq(DoubleType)
+
+ protected val n = AttributeReference("n", DoubleType, nullable = false)()
+ protected val avg = AttributeReference("avg", DoubleType, nullable =
false)()
+ protected val m2 = AttributeReference("m2", DoubleType, nullable =
false)()
+ protected val m3 = AttributeReference("m3", DoubleType, nullable =
false)()
+ protected val m4 = AttributeReference("m4", DoubleType, nullable =
false)()
+
+ private def trimHigherOrder[T](expressions: Seq[T]) =
expressions.take(momentOrder + 1)
+
+ override val aggBufferAttributes = trimHigherOrder(Seq(n, avg, m2, m3,
m4))
+
+ override val initialValues: Seq[Expression] =
+ trimHigherOrder(Seq(Literal(0.0), Literal(0.0), Literal(0.0),
Literal(0.0), Literal(0.0)))
--- End diff --
Sorry for some miscommunication. The previous inline comments are useful
here because `Lit(0.0)` carries no information. The comments are not necessary
when the variable names can clearly tell what they are. Please recover the
inline comments for initial values.
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