Github user davies commented on a diff in the pull request:
https://github.com/apache/spark/pull/10786#discussion_r50043531
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/Stddev.scala
---
@@ -79,3 +81,116 @@ case class StddevPop(
}
}
}
+
+// Compute standard deviation based on online algorithm specified here:
+// http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
+abstract class StddevAgg(child: Expression) extends DeclarativeAggregate {
--- End diff --
This is included for benchmark, could be used to replace the imperative one
(should be done in follow up PR or this one?)
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