[MINOR][MLLIB][SQL] Clean up unused variables and unused import

## What changes were proposed in this pull request?

Clean up unused variables and unused import statements, unnecessary `return` and `toArray`, and some more style improvement,  when I walk through the code examples.

## How was this patch tested?

Testet manually on local laptop.

Author: Xin Ren <iamshrek@126.com>

Closes #14836 from keypointt/codeWalkThroughML.

5 files changed, 8 insertions, 8 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/feature/Interaction.scala b/mllib/src/main/scala/org/apache/spark/ml/feature/Interaction.scala
index 96d0bdee9e..902f84f862 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/feature/Interaction.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/feature/Interaction.scala
@@ -136,7 +136,7 @@ class Interaction @Since("1.6.0") (@Since("1.6.0") override val uid: String) ext
         case _: VectorUDT =>
           val attrs = AttributeGroup.fromStructField(f).attributes.getOrElse(
             throw new SparkException("Vector attributes must be defined for interaction."))
-          attrs.map(getNumFeatures).toArray
+          attrs.map(getNumFeatures)
       }
       new FeatureEncoder(numFeatures)
     }.toArray
diff --git a/mllib/src/main/scala/org/apache/spark/ml/r/IsotonicRegressionWrapper.scala b/mllib/src/main/scala/org/apache/spark/ml/r/IsotonicRegressionWrapper.scala
index 1ea80cb46a..a7992debe6 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/r/IsotonicRegressionWrapper.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/r/IsotonicRegressionWrapper.scala
@@ -23,7 +23,7 @@ import org.json4s.JsonDSL._
 import org.json4s.jackson.JsonMethods._
 
 import org.apache.spark.ml.{Pipeline, PipelineModel}
-import org.apache.spark.ml.attribute.{AttributeGroup}
+import org.apache.spark.ml.attribute.AttributeGroup
 import org.apache.spark.ml.feature.RFormula
 import org.apache.spark.ml.regression.{IsotonicRegression, IsotonicRegressionModel}
 import org.apache.spark.ml.util._
diff --git a/mllib/src/main/scala/org/apache/spark/ml/util/stopwatches.scala b/mllib/src/main/scala/org/apache/spark/ml/util/stopwatches.scala
index e79b1f3164..e539deca4b 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/util/stopwatches.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/util/stopwatches.scala
@@ -20,7 +20,7 @@ package org.apache.spark.ml.util
 import scala.collection.mutable
 
 import org.apache.spark.SparkContext
-import org.apache.spark.util.LongAccumulator;
+import org.apache.spark.util.LongAccumulator
 
 /**
  * Abstract class for stopwatches.
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/feature/ChiSqSelector.scala b/mllib/src/main/scala/org/apache/spark/mllib/feature/ChiSqSelector.scala
index 56fb2d33c2..33a1f18bcc 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/feature/ChiSqSelector.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/feature/ChiSqSelector.scala
@@ -164,7 +164,7 @@ object ChiSqSelectorModel extends Loader[ChiSqSelectorModel] {
         case Row(feature: Int) => (feature)
       }.collect()
 
-      return new ChiSqSelectorModel(features)
+      new ChiSqSelectorModel(features)
     }
   }
 }
diff --git a/mllib/src/main/scala/org/apache/spark/mllib/random/RandomRDDs.scala b/mllib/src/main/scala/org/apache/spark/mllib/random/RandomRDDs.scala
index c2bc1f17cc..6d60136ddc 100644
--- a/mllib/src/main/scala/org/apache/spark/mllib/random/RandomRDDs.scala
+++ b/mllib/src/main/scala/org/apache/spark/mllib/random/RandomRDDs.scala
@@ -438,10 +438,10 @@ object RandomRDDs {
   @DeveloperApi
   @Since("1.6.0")
   def randomJavaRDD[T](
-    jsc: JavaSparkContext,
-    generator: RandomDataGenerator[T],
-    size: Long): JavaRDD[T] = {
-    randomJavaRDD(jsc, generator, size, 0);
+      jsc: JavaSparkContext,
+      generator: RandomDataGenerator[T],
+      size: Long): JavaRDD[T] = {
+    randomJavaRDD(jsc, generator, size, 0)
   }
 
   // TODO Generate RDD[Vector] from multivariate distributions.