added method partition to Iterable (#171)

3 files changed, 34 insertions, 3 deletions

diff --git a/src/library/scala/Iterable.scala b/src/library/scala/Iterable.scala
index 0acd9b824d..e00d41c7c8 100644
--- a/src/library/scala/Iterable.scala
+++ b/src/library/scala/Iterable.scala
@@ -187,6 +187,22 @@ trait Iterable[+A] {
     buf
   }
 
+  /** Partitions this iterable in two iterables according to a predicate.
+   *
+   *  @param p the predicate on which to partition
+   *  @return  a pair of iterables: the iterable that satisfy the predicate
+   *           <code>p</code> and the iterable that do not.
+   *           The relative order of the elements in the resulting iterables
+   *           is the same as in the original iterable.
+   */
+  def partition[T](p: A => Boolean): (Iterable[A], Iterable[A]) = {
+    val matched = new ArrayBuffer[A]
+    val failed = new ArrayBuffer[A]
+    val elems = elements
+    while (elems.hasNext) { val x = elems.next; if (p(x)) matched += x else failed += x }
+    (matched, failed)
+  }
+
   /** Returns the longest prefix of this iterable whose elements satisfy
    *  the predicate <code>p</code>.
    *
diff --git a/test/files/run/iterables.check b/test/files/run/iterables.check
index 2660f51aa5..aac90b70a9 100644
--- a/test/files/run/iterables.check
+++ b/test/files/run/iterables.check
@@ -1,2 +1,5 @@
 false
 0,1,2,3,4,5,6,7,8,9
+5,6,7,8,9
+0,2,4,6,8
+1,3,5,7,9
diff --git a/test/files/run/iterables.scala b/test/files/run/iterables.scala
index 7a29b80e8d..5fb587a323 100644
--- a/test/files/run/iterables.scala
+++ b/test/files/run/iterables.scala
@@ -8,7 +8,19 @@ object Test extends Application {
         else throw new IndexOutOfBoundsException("empty iterator")
     }
   }
-  val x = new Test(10)
-  println(x.isEmpty)
-  println(x.mkString(","))
+  {
+    val x = new Test(10)
+    println(x.isEmpty)
+    println(x.mkString(","))
+  }
+  {
+    val x = new Test(10)
+    println(x.filter(_ > 4).mkString(","))
+  }
+  {
+    val x = new Test(10)
+    val y = x.partition(_ % 2 == 0)
+    println(y._1.mkString(","))
+    println(y._2.mkString(","))
+  }
 }