HyukjinKwon commented on a change in pull request #27278:
[SPARK-30569][SQL][PYSPARK][SPARKR] Add percentile_approx DSL functions.
URL: https://github.com/apache/spark/pull/27278#discussion_r385499333
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File path: sql/core/src/main/scala/org/apache/spark/sql/functions.scala
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@@ -652,6 +652,50 @@ object functions {
*/
def min(columnName: String): Column = min(Column(columnName))
+ /**
+ * Aggregate function: Returns and array of the approximate percentile values
+ * of numeric column col at the given percentages.
+ *
+ * Each value of the percentage array must be between 0.0 and 1.0.
+ *
+ * The accuracy parameter is a positive numeric literal
+ * which controls approximation accuracy at the cost of memory.
+ * Higher value of accuracy yields better accuracy, 1.0/accuracy
+ * is the relative error of the approximation.
+ *
+ * @group agg_funcs
+ * @since 3.1.0
+ */
+ def percentile_approx(e: Column, percentage: Array[Double], accuracy: Long):
Column = {
Review comment:
Seems like the percentiles can at least be foldable expressions, e.g.:
```scala
scala> sql("select percentile_approx(1, 0.5 + 0.5)")
res5: org.apache.spark.sql.DataFrame = [percentile_approx(1, CAST((CAST(0.5
AS DECIMAL(2,1)) + CAST(0.5 AS DECIMAL(2,1))) AS DOUBLE), 10000): int]
```
I know it's pretty unlikely but still possible given that we have a set of
foldable expressions. The error message isn't completely correct because it can
accept other foldable expressions.
Other variants were not changed only due to the legacy reason.
I think we would have not had such arguments all signatures were with
`Column` at the very first place in `functions.scala`.
Also, it's completely no problem for any one in the community to say out
what they think is right .. :-). We just need to chime in which I think I am
not pretty good at 😢.
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