## What changes were proposed in this pull request?
Adding fitMultiple API to `Estimator` with default implementation. Also update have ml.tuning meta-estimators use this API.
## How was this patch tested?
Unit tests.
Author: Bago Amirbekian <bago@databricks.com>
Closes#20058 from MrBago/python-fitMultiple.
## What changes were proposed in this pull request?
Implemented UnaryTransformer in Python.
## How was this patch tested?
This patch was tested by creating a MockUnaryTransformer class in the unit tests that extends UnaryTransformer and testing that the transform function produced correct output.
Author: Ajay Saini <ajays725@gmail.com>
Closes#18746 from ajaysaini725/AddPythonUnaryTransformer.
## What changes were proposed in this pull request?
Now we have PySpark picklers for new and old vector/matrix, individually. However, they are all implemented under `PythonMLlibAPI`. To separate spark.mllib from spark.ml, we should implement the picklers of new vector/matrix under `spark.ml.python` instead.
## How was this patch tested?
Existing tests.
Author: Liang-Chi Hsieh <simonh@tw.ibm.com>
Closes#13219 from viirya/pyspark-pickler-ml.
## What changes were proposed in this pull request?
JIRA issue: https://issues.apache.org/jira/browse/SPARK-13038
1. Add load/save to PySpark Pipeline and PipelineModel
2. Add `_transfer_stage_to_java()` and `_transfer_stage_from_java()` for `JavaWrapper`.
## How was this patch tested?
Test with doctest.
Author: Xusen Yin <yinxusen@gmail.com>
Closes#11683 from yinxusen/SPARK-13038-only.
