[Minor] [SQL] Cleans up DataFrame variable names and toDF() calls

Although we've migrated to the DataFrame API, lots of code still uses `rdd` or `srdd` as local variable names. This PR tries to address these naming inconsistencies and some other minor DataFrame related style issues.

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Author: Cheng Lian <lian@databricks.com>

Closes #4670 from liancheng/df-cleanup and squashes the following commits:

3e14448 [Cheng Lian] Cleans up DataFrame variable names and toDF() calls

6 files changed, 7 insertions, 7 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/mllib/classification/NaiveBayes.scala b/mllib/src/main/scala/org/apache/spark/mllib/classification/NaiveBayes.scala
index dd7a9469d5..b11fd4f128 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/classification/NaiveBayes.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/classification/NaiveBayes.scala
@@ -102,7 +102,7 @@ object NaiveBayesModel extends Loader[NaiveBayesModel] {
       sc.parallelize(Seq(metadata), 1).saveAsTextFile(metadataPath(path))
 
       // Create Parquet data.
-      val dataRDD: DataFrame = sc.parallelize(Seq(data), 1).toDF
+      val dataRDD: DataFrame = sc.parallelize(Seq(data), 1).toDF()
       dataRDD.saveAsParquetFile(dataPath(path))
     }
 
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/classification/impl/GLMClassificationModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/classification/impl/GLMClassificationModel.scala
index 0a358f2e4f..8956189ff1 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/classification/impl/GLMClassificationModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/classification/impl/GLMClassificationModel.scala
@@ -62,7 +62,7 @@ private[classification] object GLMClassificationModel {
 
       // Create Parquet data.
       val data = Data(weights, intercept, threshold)
-      sc.parallelize(Seq(data), 1).toDF.saveAsParquetFile(Loader.dataPath(path))
+      sc.parallelize(Seq(data), 1).toDF().saveAsParquetFile(Loader.dataPath(path))
     }
 
     /**
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/regression/impl/GLMRegressionModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/regression/impl/GLMRegressionModel.scala
index 7b27aaa322..bd7e340ca2 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/regression/impl/GLMRegressionModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/regression/impl/GLMRegressionModel.scala
@@ -58,7 +58,7 @@ private[regression] object GLMRegressionModel {
 
       // Create Parquet data.
       val data = Data(weights, intercept)
-      val dataRDD: DataFrame = sc.parallelize(Seq(data), 1).toDF
+      val dataRDD: DataFrame = sc.parallelize(Seq(data), 1).toDF()
       // TODO: repartition with 1 partition after SPARK-5532 gets fixed
       dataRDD.saveAsParquetFile(Loader.dataPath(path))
     }
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala b/mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala
index 5dac62b0c4..060fd5b859 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/tree/model/DecisionTreeModel.scala
@@ -197,7 +197,7 @@ object DecisionTreeModel extends Loader[DecisionTreeModel] {
       val nodes = model.topNode.subtreeIterator.toSeq
       val dataRDD: DataFrame = sc.parallelize(nodes)
         .map(NodeData.apply(0, _))
-        .toDF
+        .toDF()
       dataRDD.saveAsParquetFile(Loader.dataPath(path))
     }
 
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/tree/model/treeEnsembleModels.scala b/mllib/src/main/scala/org/apache/spark/mllib/tree/model/treeEnsembleModels.scala
index e507f247cc..4897906aea 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/tree/model/treeEnsembleModels.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/tree/model/treeEnsembleModels.scala
@@ -289,7 +289,7 @@ private[tree] object TreeEnsembleModel {
       // Create Parquet data.
       val dataRDD = sc.parallelize(model.trees.zipWithIndex).flatMap { case (tree, treeId) =>
         tree.topNode.subtreeIterator.toSeq.map(node => NodeData(treeId, node))
-      }.toDF
+      }.toDF()
       dataRDD.saveAsParquetFile(Loader.dataPath(path))
     }
 
diff --git a/mllib/src/test/scala/org/apache/spark/ml/recommendation/ALSSuite.scala b/mllib/src/test/scala/org/apache/spark/ml/recommendation/ALSSuite.scala
index b118a8dcf1..376c3626f9 100644
--- a/mllib/src/test/scala/org/apache/spark/ml/recommendation/ALSSuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/ml/recommendation/ALSSuite.scala
@@ -358,8 +358,8 @@ class ALSSuite extends FunSuite with MLlibTestSparkContext with Logging {
       .setNumUserBlocks(numUserBlocks)
       .setNumItemBlocks(numItemBlocks)
     val alpha = als.getAlpha
-    val model = als.fit(training.toDF)
-    val predictions = model.transform(test.toDF)
+    val model = als.fit(training.toDF())
+    val predictions = model.transform(test.toDF())
       .select("rating", "prediction")
       .map { case Row(rating: Float, prediction: Float) =>
         (rating.toDouble, prediction.toDouble)