[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/regression.py b/python/pyspark/ml/regression.py
index 59d4fe3cf4..37648549de 100644
--- a/python/pyspark/ml/regression.py
+++ b/python/pyspark/ml/regression.py
@@ -389,7 +389,7 @@ class GBTParams(TreeEnsembleParams):
 @inherit_doc
 class DecisionTreeRegressor(JavaEstimator, HasFeaturesCol, HasLabelCol, HasPredictionCol,
                             DecisionTreeParams, TreeRegressorParams, HasCheckpointInterval,
-                            HasSeed):
+                            HasSeed, JavaMLWritable, JavaMLReadable):
     """
     `http://en.wikipedia.org/wiki/Decision_tree_learning Decision tree`
     learning algorithm for regression.
@@ -413,6 +413,18 @@ class DecisionTreeRegressor(JavaEstimator, HasFeaturesCol, HasLabelCol, HasPredi
     >>> test1 = sqlContext.createDataFrame([(Vectors.sparse(1, [0], [1.0]),)], ["features"])
     >>> model.transform(test1).head().prediction
     1.0
+    >>> dtr_path = temp_path + "/dtr"
+    >>> dt.save(dtr_path)
+    >>> dt2 = DecisionTreeRegressor.load(dtr_path)
+    >>> dt2.getMaxDepth()
+    2
+    >>> model_path = temp_path + "/dtr_model"
+    >>> model.save(model_path)
+    >>> model2 = DecisionTreeRegressionModel.load(model_path)
+    >>> model.numNodes == model2.numNodes
+    True
+    >>> model.depth == model2.depth
+    True
 
     .. versionadded:: 1.4.0
     """
@@ -498,7 +510,7 @@ class TreeEnsembleModels(JavaModel):
 
 
 @inherit_doc
-class DecisionTreeRegressionModel(DecisionTreeModel):
+class DecisionTreeRegressionModel(DecisionTreeModel, JavaMLWritable, JavaMLReadable):
     """
     Model fitted by DecisionTreeRegressor.