Class-based key in groupByKey?

[Michael Malak]

Is it permissible to use a custom class (as opposed to e.g. the built-in String 
or Int) for the key in groupByKey? It doesn't seem to be working for me on 
Spark 0.9.0/Scala 2.10.3:

import org.apache.spark.SparkContext
import org.apache.spark.SparkContext._

class C(val s:String) extends Serializable {
  override def equals(o: Any) = if (o.isInstanceOf[C]) o.asInstanceOf[C].s == s 
else false
  override def toString = s
}

object SimpleApp {
  def main(args: Array[String]) {
    val sc = new SparkContext("local", "Simple App", null, null)
    val r1 = sc.parallelize(Array((new C("a"),11),(new C("a"),12)))
    println("r1=" + r1.groupByKey.collect.mkString(";"))
    val r2 = sc.parallelize(Array(("a",11),("a",12)))
    println("r2=" + r2.groupByKey.collect.mkString(";"))
  }
}


Output
======
r1=(a,ArrayBuffer(11));(a,ArrayBuffer(12))
r2=(a,ArrayBuffer(11, 12))