11 files changed, 177 insertions, 10 deletions
diff --git a/src/library/scala/Enumeration.scala b/src/library/scala/Enumeration.scala
index 21f0c8fd3e..e7ce21b229 100644
--- a/src/library/scala/Enumeration.scala
+++ b/src/library/scala/Enumeration.scala
@@ -255,6 +255,7 @@ abstract class Enumeration (initial: Int) extends Serializable {
     def + (value: Value) = new ValueSet(nnIds + (value.id - bottomId))
     def - (value: Value) = new ValueSet(nnIds - (value.id - bottomId))
     def iterator = nnIds.iterator map (id => thisenum.apply(id + bottomId))
+    override def keysIteratorFrom(start: Value) = nnIds keysIteratorFrom start.id  map (id => thisenum.apply(id + bottomId))
     override def stringPrefix = thisenum + ".ValueSet"
     /** Creates a bit mask for the zero-adjusted ids in this set as a
      *  new array of longs */
diff --git a/src/library/scala/collection/BitSetLike.scala b/src/library/scala/collection/BitSetLike.scala
index d0f4e323c7..bf05331cb1 100644
--- a/src/library/scala/collection/BitSetLike.scala
+++ b/src/library/scala/collection/BitSetLike.scala
@@ -98,8 +98,10 @@ trait BitSetLike[+This <: BitSetLike[This] with SortedSet[Int]] extends SortedSe
     fromBitMaskNoCopy(a)
   }
 
-  def iterator: Iterator[Int] = new AbstractIterator[Int] {
-    private var current = 0
+  def iterator: Iterator[Int] = iteratorFrom(0)
+  
+  override def keysIteratorFrom(start: Int) = new AbstractIterator[Int] {
+    private var current = start
     private val end = nwords * WordLength
     def hasNext: Boolean = {
       while (current < end && !self.contains(current)) current += 1
diff --git a/src/library/scala/collection/SortedMapLike.scala b/src/library/scala/collection/SortedMapLike.scala
index 57ad3497c7..3c3e6095df 100644
--- a/src/library/scala/collection/SortedMapLike.scala
+++ b/src/library/scala/collection/SortedMapLike.scala
@@ -42,6 +42,7 @@ self =>
       val map = self.rangeImpl(from, until)
       new map.DefaultKeySortedSet
     }
+    override def keysIteratorFrom(start: A) = self.keysIteratorFrom(start)
   }
 
   /** Add a key/value pair to this map.
@@ -76,11 +77,17 @@ self =>
   override def filterKeys(p: A => Boolean): SortedMap[A, B] = new FilteredKeys(p) with SortedMap.Default[A, B] {
     implicit def ordering: Ordering[A] = self.ordering
     override def rangeImpl(from : Option[A], until : Option[A]): SortedMap[A, B] = self.rangeImpl(from, until).filterKeys(p)
+    override def iteratorFrom(start: A) = self iteratorFrom start filter {case (k, _) => p(k)}
+    override def keysIteratorFrom(start: A) = self keysIteratorFrom start filter p
+    override def valuesIteratorFrom(start: A) = self iteratorFrom start collect {case (k,v) if p(k) => v}
   }
   
   override def mapValues[C](f: B => C): SortedMap[A, C] = new MappedValues(f) with SortedMap.Default[A, C] {
     implicit def ordering: Ordering[A] = self.ordering
     override def rangeImpl(from : Option[A], until : Option[A]): SortedMap[A, C] = self.rangeImpl(from, until).mapValues(f)
+    override def iteratorFrom(start: A) = (self iteratorFrom start) map {case (k,v) => (k, f(v))}
+    override def keysIteratorFrom(start: A) = self keysIteratorFrom start
+    override def valuesIteratorFrom(start: A) = self valuesIteratorFrom start map f
   }
   
   /** Adds a number of elements provided by a traversable object
@@ -91,6 +98,28 @@ self =>
   override def ++[B1 >: B](xs: GenTraversableOnce[(A, B1)]): SortedMap[A, B1] =
     ((repr: SortedMap[A, B1]) /: xs.seq) (_ + _)
   
+  /**
+   * Creates an iterator over all the key/value pairs
+   * contained in this map having a key greater than or
+   * equal to `start` according to the ordering of
+   * this map. x.iteratorFrom(y) is equivalent
+   * to but often more efficient than x.from(y).iterator.
+   * 
+   * @param start The lower bound (inclusive)
+   * on the keys to be returned
+   */
+  def iteratorFrom(start: A): Iterator[(A, B)]
+  /**
+   * Creates an iterator over all the values contained in this
+   * map that are associated with a key greater than or equal to `start`
+   * according to the ordering of this map. x.valuesIteratorFrom(y) is
+   * equivalent to but often more efficient than 
+   * x.from(y).valuesIterator.
+   * 
+   * @param start The lower bound (inclusive)
+   * on the keys to be returned
+   */
+  def valuesIteratorFrom(start: A): Iterator[B]
 }
 
 
diff --git a/src/library/scala/collection/SortedSetLike.scala b/src/library/scala/collection/SortedSetLike.scala
index 71b45c72ff..6d1d1ac111 100644
--- a/src/library/scala/collection/SortedSetLike.scala
+++ b/src/library/scala/collection/SortedSetLike.scala
@@ -40,4 +40,14 @@ self =>
     case that: SortedSet[_] if that.ordering == ordering => that.hasAll(this.iterator)
     case that => super.subsetOf(that)
   }
+
+  /**
+   * Creates an iterator that contains all values from this collection
+   * greater than or equal to `start` according to the ordering of
+   * this collection. x.iteratorFrom(y) is equivalent to but will usually
+   * be more efficient than x.from(y).iterator
+   * 
+   * @param start The lower-bound (inclusive) of the iterator
+   */
+  def iteratorFrom(start: A): Iterator[A] = keysIteratorFrom(start)
 }
diff --git a/src/library/scala/collection/generic/Sorted.scala b/src/library/scala/collection/generic/Sorted.scala
index f962b26bd3..b3847fffc9 100644
--- a/src/library/scala/collection/generic/Sorted.scala
+++ b/src/library/scala/collection/generic/Sorted.scala
@@ -78,6 +78,18 @@ trait Sorted[K, +This <: Sorted[K, This]] {
     else
       until(next)
   }
+  
+  /**
+   * Creates an iterator over all the keys(or elements)  contained in this
+   * collection greater than or equal to `start`
+   * according to the ordering of this collection. x.keysIteratorFrom(y) 
+   * is equivalent to but often more efficient than 
+   * x.from(y).keysIterator.
+   * 
+   * @param start The lower bound (inclusive)
+   * on the keys to be returned
+   */
+  def keysIteratorFrom(start: K): Iterator[K]
 
   protected def hasAll(j: Iterator[K]): Boolean = {
     val i = keySet.iterator
diff --git a/src/library/scala/collection/immutable/RedBlackTree.scala b/src/library/scala/collection/immutable/RedBlackTree.scala
index 004c0ae8c6..c0d46765be 100644
--- a/src/library/scala/collection/immutable/RedBlackTree.scala
+++ b/src/library/scala/collection/immutable/RedBlackTree.scala
@@ -91,9 +91,9 @@ object RedBlackTree {
     if (tree.right ne null) _foreachKey(tree.right, f)
   }
 
-  def iterator[A, B](tree: Tree[A, B]): Iterator[(A, B)] = new EntriesIterator(tree)
-  def keysIterator[A, _](tree: Tree[A, _]): Iterator[A] = new KeysIterator(tree)
-  def valuesIterator[_, B](tree: Tree[_, B]): Iterator[B] = new ValuesIterator(tree)
+  def iterator[A, B](tree: Tree[A, B], start: Option[A] = None)(implicit ordering: Ordering[A]): Iterator[(A, B)] = new EntriesIterator(tree, start)
+  def keysIterator[A, _](tree: Tree[A, _], start: Option[A] = None)(implicit ordering: Ordering[A]): Iterator[A] = new KeysIterator(tree, start)
+  def valuesIterator[A, B](tree: Tree[A, B], start: Option[A] = None)(implicit ordering: Ordering[A]): Iterator[B] = new ValuesIterator(tree, start)
 
   @tailrec
   def nth[A, B](tree: Tree[A, B], n: Int): Tree[A, B] = {
@@ -425,7 +425,7 @@ object RedBlackTree {
     def unapply[A, B](t: BlackTree[A, B]) = Some((t.key, t.value, t.left, t.right))
   }
 
-  private[this] abstract class TreeIterator[A, B, R](root: Tree[A, B]) extends Iterator[R] {
+  private[this] abstract class TreeIterator[A, B, R](root: Tree[A, B], start: Option[A])(implicit ordering: Ordering[A]) extends Iterator[R] {
     protected[this] def nextResult(tree: Tree[A, B]): R
 
     override def hasNext: Boolean = lookahead ne null
@@ -481,7 +481,23 @@ object RedBlackTree {
       new Array[Tree[A, B]](maximumHeight)
     }
     private[this] var index = 0
-    private[this] var lookahead: Tree[A, B] = findLeftMostOrPopOnEmpty(root)
+    private[this] var lookahead: Tree[A, B] = start map startFrom getOrElse findLeftMostOrPopOnEmpty(root)
+    
+    /**
+     * Find the leftmost subtree whose key is equal to the given key, or if no such thing, 
+     * the leftmost subtree with the key that would be "next" after it according
+     * to the ordering. Along the way build up the iterator's path stack so that "next"
+     * functionality works.
+     */
+    private[this] def startFrom(key: A) : Tree[A,B] = if (root eq null) null else {
+      @tailrec def find(tree: Tree[A, B]): Tree[A, B] = 
+        if (tree == null) popNext
+        else find(
+          if (ordering.lteq(key, tree.key)) goLeft(tree)
+          else goRight(tree)
+        )      
+      find(root)
+    }
    
     private[this] def goLeft(tree: Tree[A, B]) = {
       pushNext(tree)
@@ -491,15 +507,15 @@ object RedBlackTree {
     private[this] def goRight(tree: Tree[A, B]) = tree.right
   }
 
-  private[this] class EntriesIterator[A, B](tree: Tree[A, B]) extends TreeIterator[A, B, (A, B)](tree) {
+  private[this] class EntriesIterator[A, B](tree: Tree[A, B], focus: Option[A])(implicit ordering: Ordering[A]) extends TreeIterator[A, B, (A, B)](tree, focus) {
     override def nextResult(tree: Tree[A, B]) = (tree.key, tree.value)
   }
 
-  private[this] class KeysIterator[A, B](tree: Tree[A, B]) extends TreeIterator[A, B, A](tree) {
+  private[this] class KeysIterator[A, B](tree: Tree[A, B], focus: Option[A])(implicit ordering: Ordering[A]) extends TreeIterator[A, B, A](tree, focus) {
     override def nextResult(tree: Tree[A, B]) = tree.key
   }
 
-  private[this] class ValuesIterator[A, B](tree: Tree[A, B]) extends TreeIterator[A, B, B](tree) {
+  private[this] class ValuesIterator[A, B](tree: Tree[A, B], focus: Option[A])(implicit ordering: Ordering[A]) extends TreeIterator[A, B, B](tree, focus) {
     override def nextResult(tree: Tree[A, B]) = tree.value
   }
 }
diff --git a/src/library/scala/collection/immutable/SortedMap.scala b/src/library/scala/collection/immutable/SortedMap.scala
index eb04231c55..5e833f87af 100644
--- a/src/library/scala/collection/immutable/SortedMap.scala
+++ b/src/library/scala/collection/immutable/SortedMap.scala
@@ -82,11 +82,17 @@ self =>
   override def filterKeys(p: A => Boolean): SortedMap[A, B] = new FilteredKeys(p) with SortedMap.Default[A, B] {
     implicit def ordering: Ordering[A] = self.ordering
     override def rangeImpl(from : Option[A], until : Option[A]): SortedMap[A, B] = self.rangeImpl(from, until).filterKeys(p)
+    override def iteratorFrom(start: A) = self iteratorFrom start filter {case (k, _) => p(k)} 
+    override def keysIteratorFrom(start : A) = self keysIteratorFrom start filter p
+    override def valuesIteratorFrom(start : A) = self iteratorFrom start collect {case (k,v) if p(k) => v}
   }
 
   override def mapValues[C](f: B => C): SortedMap[A, C] = new MappedValues(f) with SortedMap.Default[A, C] {
     implicit def ordering: Ordering[A] = self.ordering
     override def rangeImpl(from : Option[A], until : Option[A]): SortedMap[A, C] = self.rangeImpl(from, until).mapValues(f)
+    override def iteratorFrom(start: A) = self iteratorFrom start map {case (k, v) => (k, f(v))} 
+    override def keysIteratorFrom(start : A) = self keysIteratorFrom start
+    override def valuesIteratorFrom(start : A) = self valuesIteratorFrom start map f
   }
 
 }
diff --git a/src/library/scala/collection/immutable/TreeMap.scala b/src/library/scala/collection/immutable/TreeMap.scala
index 9a87d8636b..a6a6b75c32 100644
--- a/src/library/scala/collection/immutable/TreeMap.scala
+++ b/src/library/scala/collection/immutable/TreeMap.scala
@@ -189,9 +189,13 @@ class TreeMap[A, +B] private (tree: RB.Tree[A, B])(implicit val ordering: Orderi
    *  @return the new iterator
    */
   override def iterator: Iterator[(A, B)] = RB.iterator(tree)
+  override def iteratorFrom(start: A): Iterator[(A, B)] = RB.iterator(tree, Some(start))
 
   override def keysIterator: Iterator[A] = RB.keysIterator(tree)
+  override def keysIteratorFrom(start: A): Iterator[A] = RB.keysIterator(tree, Some(start))
+  
   override def valuesIterator: Iterator[B] = RB.valuesIterator(tree)
+  override def valuesIteratorFrom(start: A): Iterator[B] = RB.valuesIterator(tree, Some(start))
 
   override def contains(key: A): Boolean = RB.contains(tree, key)
   override def isDefinedAt(key: A): Boolean = RB.contains(tree, key)
diff --git a/src/library/scala/collection/immutable/TreeSet.scala b/src/library/scala/collection/immutable/TreeSet.scala
index 8bceb936aa..67668b3bef 100644
--- a/src/library/scala/collection/immutable/TreeSet.scala
+++ b/src/library/scala/collection/immutable/TreeSet.scala
@@ -144,6 +144,7 @@ class TreeSet[A] private (tree: RB.Tree[A, Unit])(implicit val ordering: Orderin
    *  @return the new iterator
    */
   def iterator: Iterator[A] = RB.keysIterator(tree)
+  override def keysIteratorFrom(start: A): Iterator[A] = RB.keysIterator(tree, Some(start))
 
   override def foreach[U](f: A =>  U) = RB.foreachKey(tree, f)
 
diff --git a/src/library/scala/collection/mutable/TreeSet.scala b/src/library/scala/collection/mutable/TreeSet.scala
index 5197af1b04..4fd35658fa 100644
--- a/src/library/scala/collection/mutable/TreeSet.scala
+++ b/src/library/scala/collection/mutable/TreeSet.scala
@@ -116,8 +116,25 @@ class TreeSet[A](implicit val ordering: Ordering[A]) extends SortedSet[A] with S
     resolve.avl.contains(elem, ordering)
   }
 
+  // TODO see the discussion on keysIteratorFrom
   override def iterator: Iterator[A] = resolve.avl.iterator
     .dropWhile(e => !isLeftAcceptable(from, ordering)(e))
       .takeWhile(e => isRightAcceptable(until, ordering)(e))
+  
+  // TODO because TreeSets are potentially ranged views into other TreeSets
+  // what this really needs to do is walk the whole stack of tree sets, find
+  // the highest "from", and then do a tree walk of the underlying avl tree
+  // to find that spot in max(O(stack depth), O(log tree.size)) time which
+  // should effectively be O(log size) since ranged views are rare and
+  // even more rarely deep. With the following implementation it's
+  // O(N log N) to get an iterator from a start point.  
+  // But before engaging that endeavor I think mutable.TreeSet should be
+  // based on the same immutable RedBlackTree that immutable.TreeSet is
+  // based on. There's no good reason to have these two collections based
+  // on two different balanced binary trees. That'll save
+  // having to duplicate logic for finding the starting point of a
+  // sorted binary tree iterator, logic that has already been
+  // baked into RedBlackTree.
+  override def keysIteratorFrom(start: A) = from(start).iterator
 
 }
diff --git a/test/files/run/iterator-from.scala b/test/files/run/iterator-from.scala
new file mode 100644
index 0000000000..8dc6ae4e51
--- /dev/null
+++ b/test/files/run/iterator-from.scala
@@ -0,0 +1,69 @@
+// This file tests iteratorFrom, keysIteratorFrom, and valueIteratorFrom on various sorted sets and maps
+
+import scala.util.{Random => R}
+import scala.collection._
+import scala.math.Ordered
+
+object Test extends App {
+  val maxLength = 25
+  val maxKey = 50
+  val maxValue = 50
+
+  def testSet[A <% Ordered[A]](set: SortedSet[A], list: List[A]) {
+    val distinctSorted = list.distinct.sorted
+    assertEquals("Set size wasn't the same as list sze", set.size, distinctSorted.size)
+
+    for(key <- distinctSorted) {
+      val clazz = set.getClass
+      val iteratorFrom = (set iteratorFrom key).toList
+      check(clazz, list, s"set iteratorFrom $key", s"(set from $key).iterator", iteratorFrom, (set from key).iterator.toList)
+      check(clazz, list, s"set.iteratorFrom $key", s"distinctSorted dropWhile (_ < $key)", iteratorFrom, distinctSorted dropWhile (_ < key))
+      check(clazz, list, s"set iteratorFrom $key", s"set keysIterator from $key", iteratorFrom, (set keysIteratorFrom key).toList)
+    }
+  }
+
+  def testMap[A <% Ordered[A], B](map: SortedMap[A, B], list: List[(A, B)]) {
+    val distinctSorted = distinctByKey(list).sortBy(_._1) 
+    assertEquals("Map size wasn't the same as list sze", map.size, distinctSorted.size)
+
+    for(keyValue <- distinctSorted) {
+      val key = keyValue._1
+      val clazz = map.getClass
+      val iteratorFrom = (map iteratorFrom key).toList
+      check(clazz, list, s"map iteratorFrom $key", s"(map from $key).iterator", iteratorFrom, (map from key).iterator.toList)
+      check(clazz, list, s"map iteratorFrom $key", s"distinctSorted dropWhile (_._1 < $key)", iteratorFrom, distinctSorted dropWhile (_._1 < key))
+      check(clazz, list, s"map iteratorFrom $key map (_._1)", s"map keysIteratorFrom $key", iteratorFrom map (_._1), (map keysIteratorFrom key).toList)
+      check(clazz, list, s"map iteratorFrom $key map (_._2)", s"map valuesIteratorFrom $key", iteratorFrom map (_._2), (map valuesIteratorFrom key).toList)     
+    }
+  }
+
+  def check[A](clazz: Class[_], list: List[_], m1: String, m2: String, l1: List[A], l2: List[A]) {
+    assertEquals(s"$clazz: `$m1` didn't match `$m2` on list $list", l1, l2)
+  }
+
+  def assertEquals[A](msg: String, x: A, y: A) {
+    assert(x == y, s"$msg\n1: $x\n2: $y")
+  }
+
+  def distinctByKey[A,B](list: List[(A, B)]) : List[(A,B)] = list.groupBy(_._1).map(_._2.last).toList
+
+  object Weekday extends Enumeration {
+    type Weekday = Value
+    val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
+  }
+
+  0 until maxLength foreach {length => 
+    val keyValues = (0 until length map {_ => (R nextInt maxKey, R nextInt maxValue)}).toList
+    val keys = keyValues map (_._2)
+    testSet(immutable.BitSet(keys:_*), keys)
+    testSet(immutable.TreeSet(keys:_*), keys)
+    testSet(mutable.TreeSet(keys:_*), keys)
+    val days = keys map {n => Weekday(n % Weekday.values.size)}
+    testSet(Weekday.ValueSet(days:_*), days)
+
+    val treeMap = immutable.TreeMap(keyValues:_*)
+    testMap(treeMap, keyValues)
+    testMap(treeMap.filterKeys(_ % 2 == 0), keyValues  filter (_._1 % 2 == 0))
+    testMap(treeMap mapValues (_ + 1), keyValues map {case (k,v) => (k, v + 1)})
+  }
+}