adds groupUntilChanged extension method on scala.collection.Iterable

Author: jeantil

src/main/scala/scala/collection/decorators/IterableDecorator.scala

@@ -33,4 +33,26 @@ class IterableDecorator[C, I <: IsIterable[C]](coll: C)(implicit val it: I) {
   def lazyFoldRight[B](z: B)(op: it.A => Either[B, B => B]): B =
     it(coll).iterator.lazyFoldRight(z)(op)
 
+  
+  /**
+    * Constructs an iterator where consecutive elements are accumulated as
+    * long as the output of f for each element doesn't change.
+    * <pre>
+    * Vector(1,2,2,3,3,3,2,2)
+    *     .splitBy(identity)
+    * </pre>
+    * produces
+    * <pre>
+    * Iterator(Vector(1),
+    *      Vector(2,2),
+    *      Vector(3,3,3),
+    *      Vector(2,2))
+    * </pre>
+    * @param f the function to compute a key for an element
+    * @tparam K the type of the computed key
+    * @return an iterator of sequences of the consecutive elements with the
+    *         same key in the original iterator
+    */
+    def splitBy[K, That](f: it.A => K)(implicit bf: BuildFrom[C, it.A, That]):Iterator[That] =
+      it(coll).iterator.splitBy(f).map(bf.fromSpecific(coll))
 }

src/test/scala/scala/collection/decorators/IterableDecoratorTest.scala

@@ -36,4 +36,23 @@ class IterableDecoratorTest {
     Assert.assertEquals(2, result2)
   }
 
+  @Test
+  def splitByShouldHonorEmptyIterator(): Unit ={
+    val split = Vector.empty[Int].splitBy(identity)
+    Assert.assertEquals(split.toVector, Vector.empty)
+  }
+  
+  @Test
+  def splitByShouldReturnSingleSeqWhenAllElHaveTheSameKey(): Unit ={
+    val value = Vector("1", "1", "1")
+    val split = value.splitBy(identity).toVector
+    Assert.assertEquals(split, Vector(value))
+  }
+  
+  @Test
+  def splitByShouldReturnSeqOfConsecutiveElementsWithTheSameKey(): Unit ={
+    val value = Vector("1", "2","2","3","3","3","2","2")
+    val split = value.iterator.splitBy(identity).toVector
+    Assert.assertEquals(split, Vector(Vector("1"),  Vector("2","2"), Vector("3","3","3"),  Vector("2","2")))
+  }
 }