diff --git a/core/src/main/scala/spark/rdd/CoalescedRDD.scala b/core/src/main/scala/spark/rdd/CoalescedRDD.scala
index f999e9b0ec..61c4d0c004 100644
--- a/core/src/main/scala/spark/rdd/CoalescedRDD.scala
+++ b/core/src/main/scala/spark/rdd/CoalescedRDD.scala
@@ -36,7 +36,21 @@ private[spark] case class CoalescedRDDPartition(
     oos.defaultWriteObject()
   }
 
+  /**
+   * Gets the preferred location for this coalesced RDD partition. Most parent indices should prefer this machine.
+   * @return preferred location
+   */
   def getPreferredLocation = prefLoc
+
+  /**
+   * Computes how many of the parents partitions have getPreferredLocation as one of their preferredLocations
+   * @return locality of this coalesced partition between 0 and 1
+   */
+  def localFraction :Double = {
+    var loc: Int = 0
+    parents.foreach(p => if (rdd.preferredLocations(p).contains(getPreferredLocation)) loc += 1)
+    if (parents.size == 0) 0.0 else (loc.toDouble / parents.size.toDouble)
+  }
 }
 
 /**
@@ -55,13 +69,9 @@ class CoalescedRDD[T: ClassManifest](
 
   override def getPartitions: Array[Partition] = {
     val res = mutable.ArrayBuffer[CoalescedRDDPartition]()
-    val targetLen = math.min(prev.partitions.length, maxPartitions)
     val packer = new PartitionCoalescer(maxPartitions, prev, balanceSlack)
 
-    packer.setupGroups(targetLen)   // setup the groups (bins) and preferred locations
-    packer.throwBalls()             // assign partitions (balls) to each group (bins)
-
-    for ((pg, i) <- packer.groupArr.zipWithIndex) {
+    for ((pg, i) <- packer.getPartitions.zipWithIndex) {
       val ids = pg.list.map(_.index).toArray
       res += new CoalescedRDDPartition(i, prev, ids, pg.prefLoc)
     }
@@ -86,27 +96,68 @@ class CoalescedRDD[T: ClassManifest](
     super.clearDependencies()
     prev = null
   }
+
+  /**
+   * Returns the preferred machine for the split. If split is of type CoalescedRDDPartition, then the preferred machine
+   * will be one which most parent splits prefer too.
+   * @param split
+   * @return the machine most preferred by split
+   */
+  override def getPreferredLocations(split: Partition): Seq[String] = {
+    if (split.isInstanceOf[CoalescedRDDPartition])
+      List(split.asInstanceOf[CoalescedRDDPartition].getPreferredLocation)
+    else
+      super.getPreferredLocations(split)
+  }
+
 }
 
 
 class PartitionCoalescer(maxPartitions: Int, prev: RDD[_], balanceSlack: Double) {
 
+  private def compare(o1: PartitionGroup, o2: PartitionGroup): Boolean = o1.size < o2.size
+  private def compare(o1: Option[PartitionGroup], o2: Option[PartitionGroup]): Boolean =
+    if (o1 == None) false else if (o2 == None) true else compare(o1.get, o2.get)
+
+  private val rnd = new scala.util.Random(7919) // keep this class deterministic
+
+  // each element of groupArr represents one coalesced partition
+  private val groupArr = mutable.ArrayBuffer[PartitionGroup]()
+
+  // hash used to check whether some machine is already in groupArr
+  private val groupHash = mutable.Map[String, mutable.ListBuffer[PartitionGroup]]()
+
+  // hash used for the first maxPartitions (to avoid duplicates)
+  private val initialHash = mutable.Map[Partition, Boolean]()
+
+  // determines the tradeoff between load-balancing the partitions sizes and their locality
+  // e.g. balanceSlack=0.10 means that it allows up to 10% imbalance in favor of locality
+  private val slack = (balanceSlack * prev.partitions.size).toInt
+
+  private var noLocality = true  // if true if no preferredLocations exists for parent RDD
+
+  this.setupGroups(math.min(prev.partitions.length, maxPartitions))   // setup the groups (bins) and preferred locations
+  this.throwBalls()             // assign partitions (balls) to each group (bins)
+
+  def getPartitions : Array[PartitionGroup] = groupArr.filter( pg => pg.size > 0).toArray
+
   // this class just keeps iterating and rotating infinitely over the partitions of the RDD
   // next() returns the next preferred machine that a partition is replicated on
   // the rotator first goes through the first replica copy of each partition, then second, then third
-  private class RotateLocations(prev: RDD[_]) extends Iterator[String] {
+  // the iterators return type is a tuple: (replicaString, partition)
+  private class RotateLocations(prev: RDD[_]) extends Iterator[(String, Partition)] {
 
-    private var it: Iterator[String] = resetIterator()
+    private var it: Iterator[(String, Partition)] = resetIterator()
     override val isEmpty = !it.hasNext
 
     // initializes/resets to start iterating from the beginning
     private def resetIterator() = {
       val i1 =  prev.partitions.view.map( (p: Partition) =>
-      { if (prev.preferredLocations(p).length > 0) Some(prev.preferredLocations(p)(0)) else None } )
+      { if (prev.preferredLocations(p).length > 0) Some((prev.preferredLocations(p)(0),p)) else None } )
       val i2 =  prev.partitions.view.map( (p: Partition) =>
-      { if (prev.preferredLocations(p).length > 1) Some(prev.preferredLocations(p)(1)) else None } )
+      { if (prev.preferredLocations(p).length > 1) Some((prev.preferredLocations(p)(1),p)) else None } )
       val i3 =  prev.partitions.view.map( (p: Partition) =>
-      { if (prev.preferredLocations(p).length > 2) Some(prev.preferredLocations(p)(2)) else None } )
+      { if (prev.preferredLocations(p).length > 2) Some((prev.preferredLocations(p)(2),p)) else None } )
       val res = List(i1,i2,i3)
       res.view.flatMap(x => x).flatten.iterator // fuses the 3 iterators (1st replica, 2nd, 3rd) into one iterator
     }
@@ -115,7 +166,7 @@ class PartitionCoalescer(maxPartitions: Int, prev: RDD[_], balanceSlack: Double)
     def hasNext(): Boolean = !isEmpty
 
     // return the next preferredLocation of some partition of the RDD
-    def next(): String = {
+    def next(): (String, Partition) = {
       if (it.hasNext)
         it.next()
       else {
@@ -126,42 +177,11 @@ class PartitionCoalescer(maxPartitions: Int, prev: RDD[_], balanceSlack: Double)
   }
 
   case class PartitionGroup(prefLoc: String = "") {
-    var list = mutable.MutableList[Partition]()
+    var list = mutable.ListBuffer[Partition]()
 
     def size = list.size
-
-    // returns number of partitions that got locality in this group
-    def local = {
-      var loc: Int = 0
-      list.foreach(p => if (prev.preferredLocations(p).contains(prefLoc)) loc += 1)
-      loc
-    }
-
-    override def toString(): String = {
-      val localityStr = if (size == 0) "0" else (local*100. / size).toInt.toString
-      "PartitionGroup(\"" + prefLoc + "\") size: " + size + " locality: " + localityStr +"% \n"
-      //    list.map("\t\t" + _.toString).mkString("\n") + "\n"
-    }
   }
 
-  def compare(o1: PartitionGroup, o2: PartitionGroup): Boolean = o1.size < o2.size
-  def compare(o1: Option[PartitionGroup], o2: Option[PartitionGroup]): Boolean =
-    if (o1 == None) false else if (o2 == None) true else compare(o1.get, o2.get)
-
-  val rnd = new scala.util.Random(7919) // keep this class deterministic
-
-  // each element of groupArr represents one coalesced partition
-  val groupArr = mutable.ArrayBuffer[PartitionGroup]()
-
-  // hash used to check whether some machine is already in groupArr
-  val groupHash = mutable.Map[String, mutable.MutableList[PartitionGroup]]()
-
-  // determines the tradeoff between load-balancing the partitions sizes and their locality
-  // e.g. balanceSlack=0.10 means that it allows up to 10% imbalance in favor of locality
-  val slack = (balanceSlack * prev.partitions.size).toInt
-
-  private var noLocality = true  // if true if no preferredLocations exists for parent RDD
-
   /**
    * Sorts and gets the least element of the list associated with key in groupHash
    * The returned PartitionGroup is the least loaded of all groups that represent the machine "key"
@@ -172,13 +192,21 @@ class PartitionCoalescer(maxPartitions: Int, prev: RDD[_], balanceSlack: Double)
     groupHash.get(key).map(_.sortWith(compare).head)
   }
 
+  def addPartToPGroup(part : Partition, pgroup : PartitionGroup) : Boolean = {
+    if (!initialHash.contains(part)) {
+      pgroup.list += part           // already preassign this element, ensures every bucket will have 1 element
+      initialHash += (part -> true) // needed to avoid assigning partitions to multiple buckets/groups
+      true
+    } else false
+  }
+
   /**
    * Initializes targetLen partition groups and assigns a preferredLocation
    * This uses coupon collector to estimate how many preferredLocations it must rotate through until it has seen
    * most of the preferred locations (2 * n log(n))
    * @param targetLen
    */
-  def setupGroups(targetLen: Int) {
+  private def setupGroups(targetLen: Int) {
     val rotIt = new RotateLocations(prev)
 
     // deal with empty rotator case, just create targetLen partition groups with no preferred location
@@ -199,22 +227,29 @@ class PartitionCoalescer(maxPartitions: Int, prev: RDD[_], balanceSlack: Double)
     // likely targetLen >> number of preferred locations (more buckets than there are machines)
     while (numCreated < targetLen && tries < expectedCoupons2) {
       tries += 1
-      val nxt = rotIt.next()
-      if (!groupHash.contains(nxt)) {
-        val pgroup = PartitionGroup(nxt)
+      val (nxt_replica, nxt_part) = rotIt.next()
+      if (!groupHash.contains(nxt_replica)) {
+        val pgroup = PartitionGroup(nxt_replica)
         groupArr += pgroup
-        groupHash += (nxt -> (mutable.MutableList(pgroup))) // use list in case we have multiple groups for same machine
+        addPartToPGroup(nxt_part, pgroup)
+        groupHash += (nxt_replica -> (mutable.ListBuffer(pgroup))) // list in case we have multiple groups per machine
         numCreated += 1
       }
     }
 
     while (numCreated < targetLen) {  // if we don't have enough partition groups, just create duplicates
-    val nxt = rotIt.next()
-      val pgroup = PartitionGroup(nxt)
+    var (nxt_replica, nxt_part) = rotIt.next()
+      val pgroup = PartitionGroup(nxt_replica)
       groupArr += pgroup
-      groupHash.get(nxt).get += pgroup
+      groupHash.get(nxt_replica).get += pgroup
+      var tries = 0
+      while (!addPartToPGroup(nxt_part, pgroup) && tries < targetLen) { // ensure each group has at least one partition
+        nxt_part = rotIt.next()._2
+        tries += 1
+      }
       numCreated += 1
     }
+
   }
 
   /**
@@ -224,7 +259,7 @@ class PartitionCoalescer(maxPartitions: Int, prev: RDD[_], balanceSlack: Double)
    * @param p partition (ball to be thrown)
    * @return partition group (bin to be put in)
    */
-  def pickBin(p: Partition): PartitionGroup = {
+  private def pickBin(p: Partition): PartitionGroup = {
     val pref = prev.preferredLocations(p).map(getLeastGroupHash(_)).sortWith(compare) // least loaded bin of replicas
     val prefPart = if (pref == Nil) None else pref.head
 
@@ -243,7 +278,7 @@ class PartitionCoalescer(maxPartitions: Int, prev: RDD[_], balanceSlack: Double)
     }
   }
 
-  def throwBalls() {
+  private def throwBalls() {
     if (noLocality) {  // no preferredLocations in parent RDD, no randomization needed
       if (maxPartitions > groupArr.size) { // just return prev.partitions
         for ((p,i) <- prev.partitions.zipWithIndex) {
@@ -257,7 +292,7 @@ class PartitionCoalescer(maxPartitions: Int, prev: RDD[_], balanceSlack: Double)
         }
       }
     } else {
-      for (p <- prev.partitions) { // throw every partition (ball) into a partition group (bin)
+      for (p <- prev.partitions if (!initialHash.contains(p))) { // throw every partition into a partition group
         pickBin(p).list += p
       }
     }
diff --git a/core/src/test/scala/spark/RDDSuite.scala b/core/src/test/scala/spark/RDDSuite.scala
index 881bdedfe5..c200bfe909 100644
--- a/core/src/test/scala/spark/RDDSuite.scala
+++ b/core/src/test/scala/spark/RDDSuite.scala
@@ -22,7 +22,8 @@ import org.scalatest.FunSuite
 import org.scalatest.concurrent.Timeouts._
 import org.scalatest.time.{Span, Millis}
 import spark.SparkContext._
-import spark.rdd.{CoalescedRDD, CoGroupedRDD, EmptyRDD, PartitionPruningRDD, ShuffledRDD}
+import spark.rdd._
+import scala.collection.parallel.mutable
 
 class RDDSuite extends FunSuite with SharedSparkContext {
 
@@ -184,16 +185,35 @@ class RDDSuite extends FunSuite with SharedSparkContext {
 
     assert(splits.foldLeft(true)( (x,y) => if (!x) false else y.length >= 2) === true) // descent balance (2+ per bin)
 
-    val prefs = List(List("m1","m2","m3"), List("m4","m5","m6"))
-    val data2 = sc.makeRDD((1 to 100).map( i => (i, prefs(i % 2) ))) // alternate machine prefs
-    val coalesced2 = data2.coalesce(10)
-    val splits2 = coalesced2.glom().collect().map(_.toList).toList
+    // If we try to coalesce into more partitions than the original RDD, it should just
+    // keep the original number of partitions.
+    val coalesced4 = data.coalesce(20)
+    assert(coalesced4.glom().collect().map(_.toList).toList.sortWith(
+      (x, y) => if (x.isEmpty) false else if (y.isEmpty) true else x(0) < y(0)) === (1 to 9).map(x => List(x)).toList)
 
-    // this gives a list of pairs, each pair is of the form (even,odd), where even is the number of even elements...
-    val list = splits2.map( ls => ls.foldLeft((0,0))( (x,y) => if (y % 2 == 0) (x._1+1,x._2) else (x._1,x._2+1)) )
-    val maxes = list.map( { case (a,b) => if (a>b) a else b } ) // get the maxs, this represents the locality
-    maxes.foreach( locality => assert( locality > 7) ) // at least 70% locality in each partition
 
+    // large scale experiment
+    import collection.mutable
+    val rnd = scala.util.Random
+    val partitions = 10000
+    val numMachines = 50
+    val machines = mutable.ListBuffer[String]()
+    (1 to numMachines).foreach(machines += "m"+_)
+
+    val blocks = (1 to partitions).map( i => (i, (i to (i+2)).map{ j => machines(rnd.nextInt(machines.size)) } ))
+
+    val data2 = sc.makeRDD(blocks)
+    val coalesced2 = data2.coalesce(numMachines*2)
+
+    // test that you get over 95% locality in each group
+    val minLocality = coalesced2.partitions.map( part => part.asInstanceOf[CoalescedRDDPartition].localFraction )
+      .foldLeft(100.)( (perc, loc) => math.min(perc,loc) )
+    assert(minLocality > 0.95)
+
+    // test that the groups are load balanced with 100 +/- 15 elements in each
+    val maxImbalance = coalesced2.partitions.map( part => part.asInstanceOf[CoalescedRDDPartition].parents.size )
+      .foldLeft(0)((dev, curr) => math.max(math.abs(100-curr),dev))
+    assert(maxImbalance < 15)
   }
 
   test("zipped RDDs") {