Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/14033#discussion_r69510162
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/generators.scala
---
@@ -94,6 +94,63 @@ 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 CodegenFallback {
+
+ private lazy val numRows = children.head.eval().asInstanceOf[Int]
+ private lazy val numFields = ((children.length - 1) + numRows - 1) /
numRows
--- End diff --
can you explain a bit more about this? It will be good if we can expression
the logic more clear using `math.ceil` or something.
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