[SPARK-1837] NumericRange should be partitioned in the same way as other...

... sequences

Author: Kan Zhang <kzhang@apache.org>

Closes #776 from kanzhang/SPARK-1837 and squashes the following commits:

e48f018 [Kan Zhang] [SPARK-1837] code refactoring
67c33b5 [Kan Zhang] minor change
403f9b1 [Kan Zhang] [SPARK-1837] NumericRange should be partitioned in the same way as other sequences

core/src/main/scala/org/apache/spark/rdd/ParallelCollectionRDD.scala

@@ -117,6 +117,15 @@ private object ParallelCollectionRDD {
     if (numSlices < 1) {
       throw new IllegalArgumentException("Positive number of slices required")
     }
+    // Sequences need to be sliced at the same set of index positions for operations
+    // like RDD.zip() to behave as expected
+    def positions(length: Long, numSlices: Int): Iterator[(Int, Int)] = {
+      (0 until numSlices).iterator.map(i => {
+        val start = ((i * length) / numSlices).toInt
+        val end = (((i + 1) * length) / numSlices).toInt
+        (start, end)
+      })
+    }
     seq match {
       case r: Range.Inclusive => {
         val sign = if (r.step < 0) {
@@ -128,18 +137,17 @@ private object ParallelCollectionRDD {
           r.start, r.end + sign, r.step).asInstanceOf[Seq[T]], numSlices)
       }
       case r: Range => {
-        (0 until numSlices).map(i => {
-          val start = ((i * r.length.toLong) / numSlices).toInt
-          val end = (((i + 1) * r.length.toLong) / numSlices).toInt
-          new Range(r.start + start * r.step, r.start + end * r.step, r.step)
-        }).asInstanceOf[Seq[Seq[T]]]
+        positions(r.length, numSlices).map({
+          case (start, end) =>
+            new Range(r.start + start * r.step, r.start + end * r.step, r.step)
+        }).toSeq.asInstanceOf[Seq[Seq[T]]]
       }
       case nr: NumericRange[_] => {
         // For ranges of Long, Double, BigInteger, etc
         val slices = new ArrayBuffer[Seq[T]](numSlices)
-        val sliceSize = (nr.size + numSlices - 1) / numSlices // Round up to catch everything
         var r = nr
-        for (i <- 0 until numSlices) {
+        for ((start, end) <- positions(nr.length, numSlices)) {
+          val sliceSize = end - start
           slices += r.take(sliceSize).asInstanceOf[Seq[T]]
           r = r.drop(sliceSize)
         }
@@ -147,11 +155,10 @@ private object ParallelCollectionRDD {
       }
       case _ => {
         val array = seq.toArray // To prevent O(n^2) operations for List etc
-        (0 until numSlices).map(i => {
-          val start = ((i * array.length.toLong) / numSlices).toInt
-          val end = (((i + 1) * array.length.toLong) / numSlices).toInt
-          array.slice(start, end).toSeq
-        })
+        positions(array.length, numSlices).map({
+          case (start, end) =>
+            array.slice(start, end).toSeq
+        }).toSeq
       }
     }
   }

core/src/test/scala/org/apache/spark/rdd/ParallelCollectionSplitSuite.scala

@@ -111,6 +111,24 @@ class ParallelCollectionSplitSuite extends FunSuite with Checkers {
     assert(slices.forall(_.isInstanceOf[Range]))
   }
 
+  test("identical slice sizes between Range and NumericRange") {
+    val r = ParallelCollectionRDD.slice(1 to 7, 4)
+    val nr = ParallelCollectionRDD.slice(1L to 7L, 4)
+    assert(r.size === 4)
+    for (i <- 0 until r.size) {
+      assert(r(i).size === nr(i).size)
+    }
+  }
+
+  test("identical slice sizes between List and NumericRange") {
+    val r = ParallelCollectionRDD.slice(List(1, 2), 4)
+    val nr = ParallelCollectionRDD.slice(1L to 2L, 4)
+    assert(r.size === 4)
+    for (i <- 0 until r.size) {
+      assert(r(i).size === nr(i).size)
+    }
+  }
+
   test("large ranges don't overflow") {
     val N = 100 * 1000 * 1000
     val data = 0 until N