Github user rxin commented on a diff in the pull request:

    https://github.com/apache/spark/pull/5842#discussion_r29553037
  
    --- 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 --
    
    use dataframe's own group by and count; don't use the rdd one. df one will 
get a lot faster with tungsten over time.


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