Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/10402#discussion_r48186892
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala
---
@@ -421,6 +460,19 @@ case class CumeDist() extends RowNumberLike with
SizeBasedWindowFunction {
override val evaluateExpression = Divide(Cast(rowNumber, DoubleType),
Cast(n, DoubleType))
}
+/**
+ * The NTile function divides the rows for each window partition into 'n'
buckets ranging from 1 to
+ * at most 'n'. Bucket values will differ by at most 1. If the number of
rows in the partition does
+ * not divide evenly into the number of buckets, then the remainder values
are distributed one per
+ * bucket, starting with the first bucket.
+ *
+ * The NTile function is particularly useful for the calculation of
tertiles, quartiles, deciles and
+ * other common summary statistics
+ *
+ * @param buckets number of buckets to divide the rows in.
+ */
+@ExpressionDescription(usage = "_FUNC_(x) - The NTILE(n) function divides
the rows for each " +
+ "window partition into 'n' buckets ranging from 1 to at most 'n'.")
case class NTile(buckets: Expression) extends RowNumberLike with
SizeBasedWindowFunction {
--- End diff --
Add some comments to explain the implementation of NTile?
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