Github user dongjoon-hyun commented on a diff in the pull request:
https://github.com/apache/spark/pull/14033#discussion_r69407409
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/generators.scala
---
@@ -94,6 +96,61 @@ case class UserDefinedGenerator(
}
/**
+ * Separate v1, ..., vk into n rows. Each row will have k/n columns. n
must be constant.
+ * {{{
+ * SELECT stack(2, 1, 2, 3)) ->
+ * 1 2
+ * 3 NULL
+ * }}}
+ */
+@ExpressionDescription(
+ usage = "_FUNC_(n, v1, ..., vk) - Separate v1, ..., vk into n rows.",
+ extended = "> SELECT _FUNC_(2, 1, 2, 3);\n [1,2]\n [3,null]")
+case class Stack(children: Seq[Expression])
+ extends Expression with Generator with ImplicitCastInputTypes with
CodegenFallback {
+
+ override def inputTypes: Seq[DataType] =
+ Seq(IntegerType) ++ Seq.fill(children.length -
1)(children.tail.head.dataType)
+
+ override def checkInputDataTypes(): TypeCheckResult = {
+ if (children.length <= 1) {
+ TypeCheckResult.TypeCheckFailure(s"$prettyName requires at least 2
arguments.")
+ } else if (!children.head.foldable ||
children.head.eval().asInstanceOf[Int] < 1) {
+ TypeCheckResult.TypeCheckFailure("The number of rows must be
positive constant.")
+ } else if (children.tail.map(_.dataType).distinct.count(_ != NullType)
> 1) {
+ TypeCheckResult.TypeCheckFailure(
+ s"The expressions should all have the same type," +
+ s" but got $prettyName(${children.map(_.dataType)}).")
+ } else {
+ TypeCheckResult.TypeCheckSuccess
+ }
+ }
+
+ private lazy val numRows = children.head.eval().asInstanceOf[Int]
+ private lazy val numFields = ((children.length - 1) + numRows - 1) /
numRows
+
+ override def elementSchema: StructType = {
+ var schema = new StructType()
+ for (i <- 0 until numFields) {
+ schema = schema.add(s"col$i", children(1).dataType)
+ }
+ schema
+ }
+
+ override def eval(input: InternalRow): TraversableOnce[InternalRow] = {
+ val values = children.tail.map(_.eval(input))
+ for (row <- 0 until numRows) yield {
+ val fields = ArrayBuffer.empty[Any]
--- End diff --
Right, Good catch!
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