[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

1 files changed, 2 insertions, 2 deletions

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)