Added a sequence shuffling method to scala.util...

Added a sequence shuffling method to scala.util.Random.

1 files changed, 30 insertions, 1 deletions

diff --git a/src/library/scala/util/Random.scala b/src/library/scala/util/Random.scala
index 09d15ff500..0bdf590df7 100644
--- a/src/library/scala/util/Random.scala
+++ b/src/library/scala/util/Random.scala
@@ -72,8 +72,37 @@ class Random(val self: java.util.Random) {
 }
 
 /** The object <code>Random</code> offers a default implementation
- *  of scala.util.Random.
+ *  of scala.util.Random and random-related convenience methods.
  *
  *  @since 2.8
  */
 object Random extends Random
+{
+  import collection.Sequence
+
+  /** Returns a new sequence in random order.
+   *  @param  seq   the sequence to shuffle
+   *  @return       the shuffled sequence
+   */
+  def shuffle[T](seq: Sequence[T]): Sequence[T] = {
+    // It would be better if this preserved the shape of its container, but I have
+    // again been defeated by the lack of higher-kinded type inference.  I can
+    // only make it work that way if it's called like
+    //   shuffle[Int,List](List.range(0,100))
+    // which nicely defeats the "convenience" portion of "convenience method".
+    val buf: Array[T] = seq.toArray
+
+    def swap(i1: Int, i2: Int) {
+      val tmp = buf(i1)
+      buf(i1) = buf(i2)
+      buf(i2) = tmp
+    }
+
+    for (n <- buf.length to 2 by -1) {
+      val k = nextInt(n)
+      swap(n - 1, k)
+    }
+
+    buf.toSeq
+  }
+}