Address Andrew's comments

sql/core/src/main/scala/org/apache/spark/sql/execution/local/LocalNode.scala

@@ -69,6 +69,11 @@ abstract class LocalNode(conf: SQLConf) extends TreeNode[LocalNode] with Logging
    */
   def close(): Unit
 
+  /**
+   * Returns the content through the [[Iterator]] interface.
+   */
+  final def asIterator: Iterator[InternalRow] = new LocalNodeIterator(this)
+
   /**
    * Returns the content of the iterator from the beginning to the end in the form of a Scala Seq.
    */
@@ -108,7 +113,6 @@ abstract class LocalNode(conf: SQLConf) extends TreeNode[LocalNode] with Logging
     }
   }
 
-  def toIterator: Iterator[InternalRow] = new LocalNodeIterator(this)
 }
 
 

sql/core/src/main/scala/org/apache/spark/sql/execution/local/SampleNode.scala

@@ -63,7 +63,7 @@ case class SampleNode(
         (new BernoulliCellSampler[InternalRow](lowerBound, upperBound), seed)
       }
     sampler.setSeed(_seed)
-    iterator = sampler.sample(child.toIterator)
+    iterator = sampler.sample(child.asIterator)
   }
 
   override def next(): Boolean = {

sql/core/src/main/scala/org/apache/spark/sql/execution/local/TakeOrderedAndProjectNode.scala

@@ -29,23 +29,21 @@ case class TakeOrderedAndProjectNode(
     projectList: Option[Seq[NamedExpression]],
     child: LocalNode) extends UnaryLocalNode(conf) {
 
-  override def output: Seq[Attribute] = {
-    val projectOutput = projectList.map(_.map(_.toAttribute))
-    projectOutput.getOrElse(child.output)
-  }
-
   private[this] var projection: Option[Projection] = _
-
   private[this] var ord: InterpretedOrdering = _
-
   private[this] var iterator: Iterator[InternalRow] = _
-
   private[this] var currentRow: InternalRow = _
 
+  override def output: Seq[Attribute] = {
+    val projectOutput = projectList.map(_.map(_.toAttribute))
+    projectOutput.getOrElse(child.output)
+  }
+
   override def open(): Unit = {
     child.open()
     projection = projectList.map(new InterpretedProjection(_, child.output))
     ord = new InterpretedOrdering(sortOrder, child.output)
+    // Priority keeps the largest elements, so let's reverse the ordering.
     val queue = new BoundedPriorityQueue[InternalRow](limit)(ord.reverse)
     while (child.next()) {
       queue += child.fetch()
@@ -58,7 +56,10 @@ case class TakeOrderedAndProjectNode(
   override def next(): Boolean = {
     if (iterator.hasNext) {
       val _currentRow = iterator.next()
-      currentRow = projection.map(p => p(_currentRow)).getOrElse(_currentRow)
+      currentRow = projection match {
+        case Some(p) => p(_currentRow)
+        case None => _currentRow
+      }
       true
     } else {
       false

sql/core/src/test/scala/org/apache/spark/sql/execution/local/SampleNodeSuite.scala

@@ -17,46 +17,24 @@
 
 package org.apache.spark.sql.execution.local
 
-import org.apache.spark.sql.Column
-import org.apache.spark.sql.catalyst.expressions.{Ascending, Expression, SortOrder}
-
 class SampleNodeSuite extends LocalNodeTest {
 
   import testImplicits._
 
-  def columnToSortOrder(sortExprs: Column*): Seq[SortOrder] = {
-    val sortOrder: Seq[SortOrder] = sortExprs.map { col =>
-      col.expr match {
-        case expr: SortOrder =>
-          expr
-        case expr: Expression =>
-          SortOrder(expr, Ascending)
-      }
+  private def testSample(withReplacement: Boolean): Unit = {
+    test(s"withReplacement: $withReplacement") {
+      val seed = 0L
+      val input = sqlContext.sparkContext.
+        parallelize((1 to 10).map(i => (i, i.toString)), 1). // Should be only 1 partition
+        toDF("key", "value")
+      checkAnswer(
+        input,
+        node => SampleNode(conf, 0.0, 0.3, withReplacement, seed, node),
+        input.sample(withReplacement, 0.3, seed).collect()
+      )
     }
-    sortOrder
-  }
-
-  test("withReplacement: true") {
-    val seed = 0L
-    val input = sqlContext.sparkContext.
-      parallelize((1 to 10).map(i => (i, i.toString)), 1). // Should be only 1 partition
-      toDF("key", "value")
-    checkAnswer(
-      input,
-      node => SampleNode(conf, 0.0, 0.3, true, seed, node),
-      input.sample(true, 0.3, seed).collect()
-    )
   }
 
-  test("withReplacement: false") {
-    val seed = 0L
-    val input = sqlContext.sparkContext.
-      parallelize((1 to 10).map(i => (i, i.toString)), 1). // Should be only 1 partition
-      toDF("key", "value")
-    checkAnswer(
-      input,
-      node => SampleNode(conf, 0.0, 0.3, false, seed, node),
-      input.sample(false, 0.3, seed).collect()
-    )
-  }
+  testSample(withReplacement = true)
+  testSample(withReplacement = false)
 }

sql/core/src/test/scala/org/apache/spark/sql/execution/local/TakeOrderedAndProjectNodeSuite.scala

@@ -24,7 +24,7 @@ class TakeOrderedAndProjectNodeSuite extends LocalNodeTest {
 
   import testImplicits._
 
-  def columnToSortOrder(sortExprs: Column*): Seq[SortOrder] = {
+  private def columnToSortOrder(sortExprs: Column*): Seq[SortOrder] = {
     val sortOrder: Seq[SortOrder] = sortExprs.map { col =>
       col.expr match {
         case expr: SortOrder =>
@@ -36,22 +36,19 @@ class TakeOrderedAndProjectNodeSuite extends LocalNodeTest {
     sortOrder
   }
 
-  test("asc") {
-    val input = (1 to 10).map(i => (i, i.toString)).toDF("key", "value")
-    checkAnswer(
-      input,
-      node => TakeOrderedAndProjectNode(conf, 5, columnToSortOrder(input.col("key")), None, node),
-      input.sort(input.col("key")).limit(5).collect()
-    )
+  private def testTakeOrderedAndProjectNode(desc: Boolean): Unit = {
+    val testCaseName = if (desc) "desc" else "asc"
+    test(testCaseName) {
+      val input = (1 to 10).map(i => (i, i.toString)).toDF("key", "value")
+      val sortColumn = if (desc) input.col("key").desc else input.col("key")
+      checkAnswer(
+        input,
+        node => TakeOrderedAndProjectNode(conf, 5, columnToSortOrder(sortColumn), None, node),
+        input.sort(sortColumn).limit(5).collect()
+      )
+    }
   }
 
-  test("desc") {
-    val input = (1 to 10).map(i => (i, i.toString)).toDF("key", "value")
-    checkAnswer(
-      input,
-      node =>
-        TakeOrderedAndProjectNode(conf, 5, columnToSortOrder(input.col("key").desc), None, node),
-      input.sort(input.col("key").desc).limit(5).collect()
-    )
-  }
+  testTakeOrderedAndProjectNode(desc = false)
+  testTakeOrderedAndProjectNode(desc = true)
 }