[jira] [Commented] (SPARK-16325) reduceByKey requires an implicit ordering which it never uses

["Sean Owen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-16325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15356894#comment-15356894 ] 

Sean Owen commented on SPARK-16325:
-----------------------------------

I can't reproduce that. What requires an Ordering, and what is the error? the method does not itself require any Ordering.

> reduceByKey requires an implicit ordering which it never uses
> -------------------------------------------------------------
>
>                 Key: SPARK-16325
>                 URL: https://issues.apache.org/jira/browse/SPARK-16325
>             Project: Spark
>          Issue Type: Bug
>            Reporter: Tofigh
>            Priority: Minor
>
> assume there is a case class as follows:
> case class UnorderedPair[A](left: A, right: A) extends Serializable {
>   override def equals(obj: Any): Boolean = obj match {
>     case other: UnorderedPair[A] => (this.left == other.left && this.right == other.right) || (this.left == other.right && this.right == other.left)
>     case _ => false
>   }
>   override def hashCode(): Int = left.hashCode() * right.hashCode()
>   def toSeq(): Seq[A] = Seq(left, right)
> }
> and assume an RDD of UnorderedPair and Seq(Long):
> val rdd = sc.parallelize(Seq( (UnorderedPair(12,14), Seq(123L)), (UnorderedPair(12,14), Seq(123L)) ))
> then the following code:
> rdd.reduceByKey(_ ++ _ )
> throws an error that an implicit Ordering is required.
> The dummy solution was to rewrite the case class as follows:
> case class UnorderedPair[A](left: A, right: A) extends Ordered[UnorderedPair[A]] with Serializable {
>   override def equals(obj: Any): Boolean = obj match {
>     case other: UnorderedPair[A] => (this.left == other.left && this.right == other.right) || (this.left == other.right && this.right == other.left)
>     case _ => false
>   }
>   override def hashCode(): Int = left.hashCode() * right.hashCode()
>   def toSeq(): Seq[A] = Seq(left, right)
>   override def compare(that: UnorderedPair[A]): Int = throw new Defect("This function should not be called. It is a workaround for a Spark bug in reduceByKey which requires an Ordering function.")
> }



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