further fix

Author: CodingCat

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

@@ -310,8 +310,7 @@ abstract class RDD[T: ClassTag](
    * Return a sampled subset of this RDD.
    */
   def sample(withReplacement: Boolean, fraction: Double, seed: Int): RDD[T] = {
-    require(fraction >= 0 && fraction <= Double.MaxValue,
-      "Invalid fraction value: " + fraction)
+    require(fraction >= 0.0, "Invalid fraction value: " + fraction)
     if (withReplacement) {
       new PartitionwiseSampledRDD[T, T](this, new PoissonSampler[T](fraction), seed)
     } else {

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

@@ -457,10 +457,10 @@ class RDDSuite extends FunSuite with SharedSparkContext {
 
   test("takeSample") {
     val data = sc.parallelize(1 to 100, 2)
-    val emptySet = data.filter(_ => false)
+    val emptySet = data.mapPartitions { iter => Iterator.empty }
 
     val sample = emptySet.takeSample(false, 20, 1)
-    assert(sample.size === 0)
+    assert(sample.length === 0)
     for (seed <- 1 to 5) {
       val sample = data.takeSample(withReplacement=false, 20, seed)
       assert(sample.size === 20)        // Got exactly 20 elements