[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.

4 files changed, 4 insertions, 4 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala b/sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala
index c060091c7f..93bf74d06b 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala
@@ -26,7 +26,7 @@ import org.apache.spark.api.java.JavaRDD
 import org.apache.spark.internal.Logging
 import org.apache.spark.rdd.RDD
 import org.apache.spark.sql.execution.LogicalRDD
-import org.apache.spark.sql.execution.datasources.{DataSource, LogicalRelation}
+import org.apache.spark.sql.execution.datasources.DataSource
 import org.apache.spark.sql.execution.datasources.jdbc.{JDBCPartition, JDBCPartitioningInfo, JDBCRelation}
 import org.apache.spark.sql.execution.datasources.json.{InferSchema, JacksonParser, JSONOptions}
 import org.apache.spark.sql.types.StructType
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala b/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
index 6da99ce0dd..e7dcf0f51f 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
@@ -43,7 +43,7 @@ import org.apache.spark.sql.catalyst.plans.logical._
 import org.apache.spark.sql.catalyst.util.usePrettyExpression
 import org.apache.spark.sql.execution.{FileRelation, LogicalRDD, QueryExecution, SQLExecution}
 import org.apache.spark.sql.execution.command.{CreateViewCommand, ExplainCommand}
-import org.apache.spark.sql.execution.datasources.{CreateTable, LogicalRelation}
+import org.apache.spark.sql.execution.datasources.LogicalRelation
 import org.apache.spark.sql.execution.datasources.json.JacksonGenerator
 import org.apache.spark.sql.execution.python.EvaluatePython
 import org.apache.spark.sql.streaming.{DataStreamWriter, StreamingQuery}
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala b/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
index fbf22197a1..2edf2e1972 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
@@ -1093,7 +1093,7 @@ object SQLContext {
     }
     data.map{ element =>
       new GenericInternalRow(
-        methodsToConverts.map { case (e, convert) => convert(e.invoke(element)) }.toArray[Any]
+        methodsToConverts.map { case (e, convert) => convert(e.invoke(element)) }
       ): InternalRow
     }
   }
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala
index b783d69974..348530888d 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala
@@ -61,7 +61,7 @@ import org.apache.spark.util.Utils
  *              qualified. This option only works when reading from a [[FileFormat]].
  * @param userSpecifiedSchema An optional specification of the schema of the data. When present
  *                            we skip attempting to infer the schema.
- * @param partitionColumns A list of column names that the relation is partitioned by.  When this
+ * @param partitionColumns A list of column names that the relation is partitioned by. When this
  *                         list is empty, the relation is unpartitioned.
  * @param bucketSpec An optional specification for bucketing (hash-partitioning) of the data.
  */