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From JoshRosen <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-8233][SQL] misc function: hash
Date Thu, 16 Jul 2015 00:50:02 GMT
Github user JoshRosen commented on a diff in the pull request:

    https://github.com/apache/spark/pull/6971#discussion_r34746496
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/misc.scala
---
    @@ -47,6 +47,45 @@ case class Md5(child: Expression) extends UnaryExpression with ExpectsInputTypes
     }
     
     /**
    + * A function that returns a hash value of the argument
    + */
    +case class Hash(children: Expression*) extends Expression {
    +
    +  override def foldable: Boolean = children.forall(_.foldable)
    +  override def nullable: Boolean = children(0).nullable
    +  override def dataType: DataType = IntegerType
    +
    +  override def eval(input: InternalRow): Any = {
    +    val arglist = children.map(_.eval(input).asInstanceOf[AnyRef])
    +    hashCode(arglist)
    +  }
    +
    +  def hashCode(v: Any): Int = v match {
    +    case null => 0
    +    case arr: Array[_] => {
    +      arr.foldLeft(0) { (acc, n) => acc + hashCode(n) }
    +    }
    +    case seq: Seq[_] => {
    +      seq.foldLeft(0) { (acc, n) => acc + hashCode(n) }
    +    }
    +    case m: Map[_, _] => {
    +      var res: Int = 0
    +      m.foreach { case (k, v) => res += (hashCode(k) + hashCode(v)) }
    --- End diff --
    
    The ordering of the map keys in `foreach` is not stable, so I think this may lead to unstable
hashcodes for identical maps.


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