[SPARK-16403][EXAMPLES] Cleanup to remove unused imports, consistent style, minor fixes

## What changes were proposed in this pull request?

Cleanup of examples, mostly from PySpark-ML to fix minor issues:  unused imports, style consistency, pipeline_example is a duplicate, use future print funciton, and a spelling error.

* The "Pipeline Example" is duplicated by "Simple Text Classification Pipeline" in Scala, Python, and Java.

* "Estimator Transformer Param Example" is duplicated by "Simple Params Example" in Scala, Python and Java

* Synced random_forest_classifier_example.py with Scala by adding IndexToString label converted

* Synced train_validation_split.py (in Scala ModelSelectionViaTrainValidationExample) by adjusting data split, adding grid for intercept.

* RegexTokenizer was doing nothing in tokenizer_example.py and JavaTokenizerExample.java, synced with Scala version

## How was this patch tested?
local tests and run modified examples

Author: Bryan Cutler <cutlerb@gmail.com>

Closes #14081 from BryanCutler/examples-cleanup-SPARK-16403.

1 files changed, 2 insertions, 0 deletions

diff --git a/examples/src/main/python/ml/vector_assembler_example.py b/examples/src/main/python/ml/vector_assembler_example.py
index bbfc316ff2..eac33711ad 100644
--- a/examples/src/main/python/ml/vector_assembler_example.py
+++ b/examples/src/main/python/ml/vector_assembler_example.py
@@ -33,9 +33,11 @@ if __name__ == "__main__":
     dataset = spark.createDataFrame(
         [(0, 18, 1.0, Vectors.dense([0.0, 10.0, 0.5]), 1.0)],
         ["id", "hour", "mobile", "userFeatures", "clicked"])
+
     assembler = VectorAssembler(
         inputCols=["hour", "mobile", "userFeatures"],
         outputCol="features")
+
     output = assembler.transform(dataset)
     print(output.select("features", "clicked").first())
     # $example off$