[SPARK-13032][ML][PYSPARK] PySpark support model export/import and take LinearRegression as example

* Implement ```MLWriter/MLWritable/MLReader/MLReadable``` for PySpark.
* Making ```LinearRegression``` to support ```save/load``` as example. After this merged, the work for other transformers/estimators will be easy, then we can list and distribute the tasks to the community.

cc mengxr jkbradley

Author: Yanbo Liang <ybliang8@gmail.com>
Author: Joseph K. Bradley <joseph@databricks.com>

Closes #10469 from yanboliang/spark-11939.

1 files changed, 24 insertions, 0 deletions

diff --git a/python/pyspark/ml/param/__init__.py b/python/pyspark/ml/param/__init__.py
index 3da36d32c5..ea86d6aeb8 100644
--- a/python/pyspark/ml/param/__init__.py
+++ b/python/pyspark/ml/param/__init__.py
@@ -314,3 +314,27 @@ class Params(Identifiable):
             if p in paramMap and to.hasParam(p.name):
                 to._set(**{p.name: paramMap[p]})
         return to
+
+    def _resetUid(self, newUid):
+        """
+        Changes the uid of this instance. This updates both
+        the stored uid and the parent uid of params and param maps.
+        This is used by persistence (loading).
+        :param newUid: new uid to use
+        :return: same instance, but with the uid and Param.parent values
+                 updated, including within param maps
+        """
+        self.uid = newUid
+        newDefaultParamMap = dict()
+        newParamMap = dict()
+        for param in self.params:
+            newParam = copy.copy(param)
+            newParam.parent = newUid
+            if param in self._defaultParamMap:
+                newDefaultParamMap[newParam] = self._defaultParamMap[param]
+            if param in self._paramMap:
+                newParamMap[newParam] = self._paramMap[param]
+            param.parent = newUid
+        self._defaultParamMap = newDefaultParamMap
+        self._paramMap = newParamMap
+        return self