[SPARK-13949][ML][PYTHON] PySpark ml DecisionTreeClassifier, Regressor support export/import

## What changes were proposed in this pull request?

Added MLReadable and MLWritable to Decision Tree Classifier and Regressor. Added doctests.

## How was this patch tested?

Python Unit tests. Tests added to check persistence in DecisionTreeClassifier and DecisionTreeRegressor.

Author: GayathriMurali <gayathri.m.softie@gmail.com>

Closes #11892 from GayathriMurali/SPARK-13949.

1 files changed, 14 insertions, 2 deletions

diff --git a/python/pyspark/ml/classification.py b/python/pyspark/ml/classification.py
index 850d775db0..d51b80e16c 100644
--- a/python/pyspark/ml/classification.py
+++ b/python/pyspark/ml/classification.py
@@ -278,7 +278,8 @@ class GBTParams(TreeEnsembleParams):
 @inherit_doc
 class DecisionTreeClassifier(JavaEstimator, HasFeaturesCol, HasLabelCol, HasPredictionCol,
                              HasProbabilityCol, HasRawPredictionCol, DecisionTreeParams,
-                             TreeClassifierParams, HasCheckpointInterval, HasSeed):
+                             TreeClassifierParams, HasCheckpointInterval, HasSeed, JavaMLWritable,
+                             JavaMLReadable):
     """
     `http://en.wikipedia.org/wiki/Decision_tree_learning Decision tree`
     learning algorithm for classification.
@@ -313,6 +314,17 @@ class DecisionTreeClassifier(JavaEstimator, HasFeaturesCol, HasLabelCol, HasPred
     >>> model.transform(test1).head().prediction
     1.0
 
+    >>> dtc_path = temp_path + "/dtc"
+    >>> dt.save(dtc_path)
+    >>> dt2 = DecisionTreeClassifier.load(dtc_path)
+    >>> dt2.getMaxDepth()
+    2
+    >>> model_path = temp_path + "/dtc_model"
+    >>> model.save(model_path)
+    >>> model2 = DecisionTreeClassificationModel.load(model_path)
+    >>> model.featureImportances == model2.featureImportances
+    True
+
     .. versionadded:: 1.4.0
     """
 
@@ -361,7 +373,7 @@ class DecisionTreeClassifier(JavaEstimator, HasFeaturesCol, HasLabelCol, HasPred
 
 
 @inherit_doc
-class DecisionTreeClassificationModel(DecisionTreeModel):
+class DecisionTreeClassificationModel(DecisionTreeModel, JavaMLWritable, JavaMLReadable):
     """
     Model fitted by DecisionTreeClassifier.