Github user HyukjinKwon commented on a diff in the pull request: https://github.com/apache/spark/pull/21982#discussion_r208491880 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/higherOrderFunctions.scala --- @@ -270,3 +278,90 @@ case class ArrayFilter( override def prettyName: String = "filter" } + +/** + * Applies a binary operator to a start value and all elements in the array. + */ +@ExpressionDescription( + usage = + """ + _FUNC_(expr, start, merge, finish) - Applies a binary operator to an initial state and all + elements in the array, and reduces this to a single state. The final state is converted + into the final result by applying a finish function. + """, + examples = """ + Examples: + > SELECT _FUNC_(array(1, 2, 3), (acc, x) -> acc + x); --- End diff -- @ueshin, would you mind if I ask to kindly double check if the example works? seems not in my local: ``` spark-sql> SELECT aggregate(array(1, 2, 3), (acc, x) -> acc + x); 2018-08-08 16:08:25 ERROR SparkSQLDriver:91 - Failed in [SELECT aggregate(array(1, 2, 3), (acc, x) -> acc + x)] org.apache.spark.sql.catalyst.analysis.UnresolvedException: Invalid call to dataType on unresolved object, tree: 'acc at org.apache.spark.sql.catalyst.analysis.UnresolvedAttribute.dataType(unresolved.scala:105) at org.apache.spark.sql.catalyst.expressions.BinaryArithmetic.dataType(arithmetic.scala:119) at org.apache.spark.sql.catalyst.expressions.LambdaFunction.dataType(higherOrderFunctions.scala:72) at org.apache.spark.sql.hive.HiveSessionCatalog$$anonfun$1.apply(HiveSessionCatalog.scala:122) at org.apache.spark.sql.hive.HiveSessionCatalog$$anonfun$1.apply(HiveSessionCatalog.scala:121) at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234) at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234) at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59) at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48) at scala.collection.TraversableLike$class.map(TraversableLike.scala:234) at scala.collection.AbstractTraversable.map(Traversable.scala:104) ```
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