SPARK-1438 RDD language apis to support optional seed in RDD methods sample/takeSample

Author: arun-rama

core/src/main/scala/org/apache/spark/api/java/JavaDoubleRDD.scala

@@ -133,7 +133,13 @@ class JavaDoubleRDD(val srdd: RDD[scala.Double]) extends JavaRDDLike[JDouble, Ja
   /**
    * Return a sampled subset of this RDD.
    */
-  def sample(withReplacement: Boolean, fraction: JDouble, seed: Int): JavaDoubleRDD =
+  def sample(withReplacement: Boolean, fraction: JDouble): JavaDoubleRDD =
+    sample(withReplacement, fraction, System.nanoTime)
+    
+  /**
+   * Return a sampled subset of this RDD.
+   */
+  def sample(withReplacement: Boolean, fraction: JDouble, seed: Long): JavaDoubleRDD =
     fromRDD(srdd.sample(withReplacement, fraction, seed))
 
   /**

core/src/main/scala/org/apache/spark/api/java/JavaPairRDD.scala

@@ -119,7 +119,13 @@ class JavaPairRDD[K, V](val rdd: RDD[(K, V)])
   /**
    * Return a sampled subset of this RDD.
    */
-  def sample(withReplacement: Boolean, fraction: Double, seed: Int): JavaPairRDD[K, V] =
+  def sample(withReplacement: Boolean, fraction: Double): JavaPairRDD[K, V] =
+    sample(withReplacement, fraction, System.nanoTime)
+    
+  /**
+   * Return a sampled subset of this RDD.
+   */
+  def sample(withReplacement: Boolean, fraction: Double, seed: Long): JavaPairRDD[K, V] =
     new JavaPairRDD[K, V](rdd.sample(withReplacement, fraction, seed))
 
   /**

core/src/main/scala/org/apache/spark/api/java/JavaRDD.scala

@@ -98,7 +98,13 @@ class JavaRDD[T](val rdd: RDD[T])(implicit val classTag: ClassTag[T])
   /**
    * Return a sampled subset of this RDD.
    */
-  def sample(withReplacement: Boolean, fraction: Double, seed: Int): JavaRDD[T] =
+  def sample(withReplacement: Boolean, fraction: Double): JavaRDD[T] =
+    sample(withReplacement, fraction, System.nanoTime)
+    
+  /**
+   * Return a sampled subset of this RDD.
+   */
+  def sample(withReplacement: Boolean, fraction: Double, seed: Long): JavaRDD[T] =
     wrapRDD(rdd.sample(withReplacement, fraction, seed))
 
   /**

core/src/main/scala/org/apache/spark/api/java/JavaRDDLike.scala

@@ -394,7 +394,10 @@ trait JavaRDDLike[T, This <: JavaRDDLike[T, This]] extends Serializable {
     new java.util.ArrayList(arr)
   }
 
-  def takeSample(withReplacement: Boolean, num: Int, seed: Int): JList[T] = {
+  def takeSample(withReplacement: Boolean, num: Int): JList[T] = 
+    takeSample(withReplacement, num, System.nanoTime)
+    
+  def takeSample(withReplacement: Boolean, num: Int, seed: Long): JList[T] = {
     import scala.collection.JavaConversions._
     val arr: java.util.Collection[T] = rdd.takeSample(withReplacement, num, seed).toSeq
     new java.util.ArrayList(arr)

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

@@ -321,7 +321,7 @@ abstract class RDD[T: ClassTag](
   /**
    * Return a sampled subset of this RDD.
    */
-  def sample(withReplacement: Boolean, fraction: Double, seed: Int): RDD[T] = {
+  def sample(withReplacement: Boolean, fraction: Double, seed: Long = System.nanoTime): RDD[T] = {
     require(fraction >= 0.0, "Invalid fraction value: " + fraction)
     if (withReplacement) {
       new PartitionwiseSampledRDD[T, T](this, new PoissonSampler[T](fraction), seed)
@@ -346,7 +346,7 @@ abstract class RDD[T: ClassTag](
     }.toArray
   }
 
-  def takeSample(withReplacement: Boolean, num: Int, seed: Int): Array[T] = {
+  def takeSample(withReplacement: Boolean, num: Int, seed: Long = System.nanoTime): Array[T] = {
     var fraction = 0.0
     var total = 0
     val multiplier = 3.0

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

@@ -466,6 +466,12 @@ class RDDSuite extends FunSuite with SharedSparkContext {
   test("takeSample") {
     val data = sc.parallelize(1 to 100, 2)
 
+    	for (num <- List(5,20,100)) {
+    	  val sample = data.takeSample(withReplacement=false, num=num)
+      assert(sample.size === num)        // Got exactly num elements
+      assert(sample.toSet.size === num)  // Elements are distinct
+      assert(sample.forall(x => 1 <= x && x <= 100), "elements not in [1, 100]")
+    	}
     for (seed <- 1 to 5) {
       val sample = data.takeSample(withReplacement=false, 20, seed)
       assert(sample.size === 20)        // Got exactly 20 elements
@@ -483,6 +489,19 @@ class RDDSuite extends FunSuite with SharedSparkContext {
       assert(sample.size === 20)        // Got exactly 20 elements
       assert(sample.forall(x => 1 <= x && x <= 100), "elements not in [1, 100]")
     }
+    {
+      val sample = data.takeSample(withReplacement=true, num=20)
+      assert(sample.size === 20)        // Got exactly 100 elements
+      assert(sample.toSet.size <= 20, "sampling with replacement returned all distinct elements")
+      assert(sample.forall(x => 1 <= x && x <= 100), "elements not in [1, 100]")
+    }
+    {
+      val sample = data.takeSample(withReplacement=true, num=100)
+      assert(sample.size === 100)        // Got exactly 100 elements
+      // Chance of getting all distinct elements is astronomically low, so test we got < 100
+      assert(sample.toSet.size < 100, "sampling with replacement returned all distinct elements")
+      assert(sample.forall(x => 1 <= x && x <= 100), "elements not in [1, 100]")
+    }
     for (seed <- 1 to 5) {
       val sample = data.takeSample(withReplacement=true, 100, seed)
       assert(sample.size === 100)        // Got exactly 100 elements

python/pyspark/rdd.py

@@ -30,6 +30,7 @@
 from threading import Thread
 import warnings
 import heapq
+import random
 
 from pyspark.serializers import NoOpSerializer, CartesianDeserializer, \
     BatchedSerializer, CloudPickleSerializer, PairDeserializer, pack_long
@@ -332,7 +333,7 @@ def distinct(self):
                    .reduceByKey(lambda x, _: x) \
                    .map(lambda (x, _): x)
 
-    def sample(self, withReplacement, fraction, seed):
+    def sample(self, withReplacement, fraction, seed=None):
         """
         Return a sampled subset of this RDD (relies on numpy and falls back
         on default random generator if numpy is unavailable).
@@ -344,7 +345,7 @@ def sample(self, withReplacement, fraction, seed):
         return self.mapPartitionsWithIndex(RDDSampler(withReplacement, fraction, seed).func, True)
 
     # this is ported from scala/spark/RDD.scala
-    def takeSample(self, withReplacement, num, seed):
+    def takeSample(self, withReplacement, num, seed=None):
         """
         Return a fixed-size sampled subset of this RDD (currently requires numpy).
 
@@ -381,13 +382,11 @@ def takeSample(self, withReplacement, num, seed):
         # If the first sample didn't turn out large enough, keep trying to take samples;
         # this shouldn't happen often because we use a big multiplier for their initial size.
         # See: scala/spark/RDD.scala
+        random.seed(seed)
         while len(samples) < total:
-            if seed > sys.maxint - 2:
-                seed = -1
-            seed += 1
-            samples = self.sample(withReplacement, fraction, seed).collect()
+            samples = self.sample(withReplacement, fraction, random.randint(0,sys.maxint)).collect()
 
-        sampler = RDDSampler(withReplacement, fraction, seed+1)
+        sampler = RDDSampler(withReplacement, fraction, random.randint(0,sys.maxint))
         sampler.shuffle(samples)
         return samples[0:total]
 

python/pyspark/rddsampler.py

@@ -19,7 +19,7 @@
 import random
 
 class RDDSampler(object):
-    def __init__(self, withReplacement, fraction, seed):
+    def __init__(self, withReplacement, fraction, seed=None):
         try:
             import numpy
             self._use_numpy = True

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicOperators.scala

@@ -168,7 +168,7 @@ case class LowerCaseSchema(child: LogicalPlan) extends UnaryNode {
   def references = Set.empty
 }
 
-case class Sample(fraction: Double, withReplacement: Boolean, seed: Int, child: LogicalPlan)
+case class Sample(fraction: Double, withReplacement: Boolean, seed: Long, child: LogicalPlan)
     extends UnaryNode {
 
   def output = child.output

sql/core/src/main/scala/org/apache/spark/sql/SchemaRDD.scala

@@ -256,10 +256,11 @@ class SchemaRDD(
    * @group Query
    */
   @Experimental
+  override
   def sample(
-      fraction: Double,
       withReplacement: Boolean = true,
-      seed: Int = (math.random * 1000).toInt) =
+      fraction: Double,
+      seed: Long) =
     new SchemaRDD(sqlContext, Sample(fraction, withReplacement, seed, logicalPlan))
 
   /**