[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, 64 insertions, 3 deletions

diff --git a/docs/ml-classification-regression.md b/docs/ml-classification-regression.md
index bb9390fd82..782ee58188 100644
--- a/docs/ml-classification-regression.md
+++ b/docs/ml-classification-regression.md
@@ -75,6 +75,13 @@ More details on parameters can be found in the [Python API documentation](api/py
 {% include_example python/ml/logistic_regression_with_elastic_net.py %}
 </div>
 
+<div data-lang="r" markdown="1">
+
+More details on parameters can be found in the [R API documentation](api/R/spark.logit.html).
+
+{% include_example binomial r/ml/logit.R %}
+</div>
+
 </div>
 
 The `spark.ml` implementation of logistic regression also supports
@@ -171,6 +178,13 @@ model with elastic net regularization.
 {% include_example python/ml/multiclass_logistic_regression_with_elastic_net.py %}
 </div>
 
+<div data-lang="r" markdown="1">
+
+More details on parameters can be found in the [R API documentation](api/R/spark.logit.html).
+
+{% include_example multinomial r/ml/logit.R %}
+</div>
+
 </div>
 
 
@@ -242,6 +256,14 @@ Refer to the [Python API docs](api/python/pyspark.ml.html#pyspark.ml.classificat
 
 {% include_example python/ml/random_forest_classifier_example.py %}
 </div>
+
+<div data-lang="r" markdown="1">
+
+Refer to the [R API docs](api/R/spark.randomForest.html) for more details.
+
+{% include_example classification r/ml/randomForest.R %}
+</div>
+
 </div>
 
 ## Gradient-boosted tree classifier
@@ -275,6 +297,14 @@ Refer to the [Python API docs](api/python/pyspark.ml.html#pyspark.ml.classificat
 
 {% include_example python/ml/gradient_boosted_tree_classifier_example.py %}
 </div>
+
+<div data-lang="r" markdown="1">
+
+Refer to the [R API docs](api/R/spark.gbt.html) for more details.
+
+{% include_example classification r/ml/gbt.R %}
+</div>
+
 </div>
 
 ## Multilayer perceptron classifier
@@ -324,6 +354,13 @@ Refer to the [Python API docs](api/python/pyspark.ml.html#pyspark.ml.classificat
 {% include_example python/ml/multilayer_perceptron_classification.py %}
 </div>
 
+<div data-lang="r" markdown="1">
+
+Refer to the [R API docs](api/R/spark.mlp.html) for more details.
+
+{% include_example r/ml/mlp.R %}
+</div>
+
 </div>
 
 
@@ -400,7 +437,7 @@ Refer to the [Python API docs](api/python/pyspark.ml.html#pyspark.ml.classificat
 
 Refer to the [R API docs](api/R/spark.naiveBayes.html) for more details.
 
-{% include_example naiveBayes r/ml.R %}
+{% include_example r/ml/naiveBayes.R %}
 </div>
 
 </div>
@@ -584,7 +621,7 @@ Refer to the [Python API docs](api/python/pyspark.ml.html#pyspark.ml.regression.
 
 Refer to the [R API docs](api/R/spark.glm.html) for more details.
 
-{% include_example glm r/ml.R %}
+{% include_example r/ml/glm.R %}
 </div>
 
 </div>
@@ -656,6 +693,14 @@ Refer to the [Python API docs](api/python/pyspark.ml.html#pyspark.ml.regression.
 
 {% include_example python/ml/random_forest_regressor_example.py %}
 </div>
+
+<div data-lang="r" markdown="1">
+
+Refer to the [R API docs](api/R/spark.randomForest.html) for more details.
+
+{% include_example regression r/ml/randomForest.R %}
+</div>
+
 </div>
 
 ## Gradient-boosted tree regression
@@ -689,6 +734,14 @@ Refer to the [Python API docs](api/python/pyspark.ml.html#pyspark.ml.regression.
 
 {% include_example python/ml/gradient_boosted_tree_regressor_example.py %}
 </div>
+
+<div data-lang="r" markdown="1">
+
+Refer to the [R API docs](api/R/spark.gbt.html) for more details.
+
+{% include_example regression r/ml/gbt.R %}
+</div>
+
 </div>
 
 
@@ -780,7 +833,7 @@ Refer to the [Python API docs](api/python/pyspark.ml.html#pyspark.ml.regression.
 
 Refer to the [R API docs](api/R/spark.survreg.html) for more details.
 
-{% include_example survreg r/ml.R %}
+{% include_example r/ml/survreg.R %}
 </div>
 
 </div>
@@ -853,6 +906,14 @@ Refer to the [`IsotonicRegression` Python docs](api/python/pyspark.ml.html#pyspa
 
 {% include_example python/ml/isotonic_regression_example.py %}
 </div>
+
+<div data-lang="r" markdown="1">
+
+Refer to the [`IsotonicRegression` R API docs](api/R/spark.isoreg.html) for more details on the API.
+
+{% include_example r/ml/isoreg.R %}
+</div>
+
 </div>
 
 # Linear methods