[SPARK-18325][SPARKR][ML] SparkR ML wrappers example code and user guide

## What changes were proposed in this pull request?
* Add all R examples for ML wrappers which were added during 2.1 release cycle.
* Split the whole ```ml.R``` example file into individual example for each algorithm, which will be convenient for users to rerun them.
* Add corresponding examples to ML user guide.
* Update ML section of SparkR user guide.

Note: MLlib Scala/Java/Python examples will be consistent, however, SparkR examples may different from them, since R users may use the algorithms in a different way, for example, using R ```formula``` to specify ```featuresCol``` and ```labelCol```.

## How was this patch tested?
Run all examples manually.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #16148 from yanboliang/spark-18325.

1 files changed, 41 insertions, 0 deletions

diff --git a/examples/src/main/r/ml/naiveBayes.R b/examples/src/main/r/ml/naiveBayes.R
new file mode 100644
index 0000000000..9c416599b4
--- /dev/null
+++ b/examples/src/main/r/ml/naiveBayes.R
@@ -0,0 +1,41 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# To run this example use
+# ./bin/spark-submit examples/src/main/r/ml/naiveBayes.R
+
+# Load SparkR library into your R session
+library(SparkR)
+
+# Initialize SparkSession
+sparkR.session(appName = "SparkR-ML-naiveBayes-example")
+
+# $example on$
+# Fit a Bernoulli naive Bayes model with spark.naiveBayes
+titanic <- as.data.frame(Titanic)
+titanicDF <- createDataFrame(titanic[titanic$Freq > 0, -5])
+nbDF <- titanicDF
+nbTestDF <- titanicDF
+nbModel <- spark.naiveBayes(nbDF, Survived ~ Class + Sex + Age)
+
+# Model summary
+summary(nbModel)
+
+# Prediction
+nbPredictions <- predict(nbModel, nbTestDF)
+showDF(nbPredictions)
+# $example off$