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

    https://github.com/apache/spark/pull/18113#discussion_r118821260
  
    --- Diff: 
sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/typedaggregators.scala
 ---
    @@ -99,3 +97,67 @@ class TypedAverage[IN](val f: IN => Double) extends 
Aggregator[IN, (Double, Long
         toColumn.asInstanceOf[TypedColumn[IN, java.lang.Double]]
       }
     }
    +
    +class TypedMinDouble[IN](val f: IN => Double) extends Aggregator[IN, 
Double, Double] {
    +  override def zero: Double = Double.PositiveInfinity
    --- End diff --
    
    We can apply an aggregate on a dataset without groupBy. E.g.,
    
        val ds = Seq.empty[(Int, Int)].toDS
        ds.agg(typed.sum((x: (Int, Int))=> x._2)).show()
    
    In this case, seems this typed `TypedMinDouble` will return the initial 
value from the `zero` variable. I've not tried it, but looks like it will get 
`Double.PositiveInfinity`. Beside the fact it's inconsistent with 
`aggregate.Min`, getting positive infinity here can't be a correct result too.


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