Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/5842#discussion_r29553039
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/stat/StatFunctions.scala
---
@@ -77,4 +78,42 @@ private[sql] object StatFunctions {
})
counts.cov
}
+
+ /** Generate a table of frequencies for the elements of two columns. */
+ private[sql] def crossTabulate(df: DataFrame, col1: String, col2:
String): DataFrame = {
+ val tableName = s"${col1}_$col2"
+ val distinctCol2 =
df.select(col2).distinct.collect().sortBy(_.get(0).toString)
--- End diff --
@mengxr what did you mean that we need two passes? If I understand this
correctly, it is simply
"select col1, col2, count(*) from table group by col1, col2"
and then pivot the result to put col2 as the colum name ? This is one pass.
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