Github user adrian-wang commented on a diff in the pull request: https://github.com/apache/spark/pull/2082#discussion_r16881896 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypes.scala --- @@ -101,3 +101,41 @@ case class GetField(child: Expression, fieldName: String) extends UnaryExpressio override def toString = s"$child.$fieldName" } + +/** + * Returns an array containing the value of fieldName + * for each element in the input array of type struct + */ +case class GetArrayField(child: Expression, fieldName: String) extends UnaryExpression { + type EvaluatedType = Any + + def dataType = field.dataType + override def nullable = child.nullable || field.nullable + override def foldable = child.foldable + + protected def arrayType = child.dataType match { + case ArrayType(s: StructType, _) => s + case otherType => sys.error(s"GetArrayField is not valid on fields of type $otherType") + } + + lazy val field = if (arrayType.isInstanceOf[StructType]) { + arrayType.fields + .find(_.name == fieldName) + .getOrElse(sys.error(s"No such field $fieldName in ${child.dataType}")) + } else null + + + lazy val ordinal = arrayType.fields.indexOf(field) + + override lazy val resolved = childrenResolved && child.dataType.isInstanceOf[ArrayType] + + override def eval(input: Row): Any = { + val value : Seq[Row] = child.eval(input).asInstanceOf[Seq[Row]] + val v = value.map{ t => + if (t == null) null else t(ordinal) + } + v --- End diff -- you can just use value.map{ t => if (t == null) null else t(ordinal) } as the last line of this `eval` function.
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