[SPARK-13786][ML][PYSPARK] Add save/load for pyspark.ml.tuning

## What changes were proposed in this pull request?

https://issues.apache.org/jira/browse/SPARK-13786

Add save/load for Python CrossValidator/Model and TrainValidationSplit/Model.

## How was this patch tested?

Test with Python doctest.

Author: Xusen Yin <yinxusen@gmail.com>

Closes #12020 from yinxusen/SPARK-13786.

1 files changed, 23 insertions, 0 deletions

diff --git a/python/pyspark/ml/wrapper.py b/python/pyspark/ml/wrapper.py
index 35b0eba926..ca93bf7d7d 100644
--- a/python/pyspark/ml/wrapper.py
+++ b/python/pyspark/ml/wrapper.py
@@ -76,6 +76,17 @@ class JavaWrapper(Params):
                 pair = self._make_java_param_pair(param, paramMap[param])
                 self._java_obj.set(pair)
 
+    def _transfer_param_map_to_java(self, pyParamMap):
+        """
+        Transforms a Python ParamMap into a Java ParamMap.
+        """
+        paramMap = JavaWrapper._new_java_obj("org.apache.spark.ml.param.ParamMap")
+        for param in self.params:
+            if param in pyParamMap:
+                pair = self._make_java_param_pair(param, pyParamMap[param])
+                paramMap.put([pair])
+        return paramMap
+
     def _transfer_params_from_java(self):
         """
         Transforms the embedded params from the companion Java object.
@@ -88,6 +99,18 @@ class JavaWrapper(Params):
                     value = _java2py(sc, self._java_obj.getOrDefault(java_param))
                     self._paramMap[param] = value
 
+    def _transfer_param_map_from_java(self, javaParamMap):
+        """
+        Transforms a Java ParamMap into a Python ParamMap.
+        """
+        sc = SparkContext._active_spark_context
+        paramMap = dict()
+        for pair in javaParamMap.toList():
+            param = pair.param()
+            if self.hasParam(str(param.name())):
+                paramMap[self.getParam(param.name())] = _java2py(sc, pair.value())
+        return paramMap
+
     @staticmethod
     def _empty_java_param_map():
         """