### What changes were proposed in this pull request?
The Experimental and Evolving annotations are both (like Unstable) used to express that a an API may change. However there are many things in the code that have been marked that way since even Spark 1.x. Per the dev thread, anything introduced at or before Spark 2.3.0 is pretty much 'stable' in that it would not change without a deprecation cycle. Therefore I'd like to remove most of these annotations. And, remove the `:: Experimental ::` scaladoc tag too. And likewise for Python, R.
The changes below can be summarized as:
- Generally, anything introduced at or before Spark 2.3.0 has been unmarked as neither Evolving nor Experimental
- Obviously experimental items like DSv2, Barrier mode, ExperimentalMethods are untouched
- I _did_ unmark a few MLlib classes introduced in 2.4, as I am quite confident they're not going to change (e.g. KolmogorovSmirnovTest, PowerIterationClustering)
It's a big change to review, so I'd suggest scanning the list of _files_ changed to see if any area seems like it should remain partly experimental and examine those.
### Why are the changes needed?
Many of these annotations are incorrect; the APIs are de facto stable. Leaving them also makes legitimate usages of the annotations less meaningful.
### Does this PR introduce any user-facing change?
No.
### How was this patch tested?
Existing tests.
Closes#25558 from srowen/SPARK-28855.
Authored-by: Sean Owen <sean.owen@databricks.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>
## 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.
