zero323 opened a new pull request #26023: [SPARK-28985][PYTHON][ML][FOLLOW-UP] 
Add _IsotonicRegressionBase
URL: https://github.com/apache/spark/pull/26023
 
 
   ### What changes were proposed in this pull request?
   
   Adds 
   
   ```python
   class _IsotonicRegressionBase(HasFeaturesCol, HasLabelCol, HasPredictionCol, 
HasWeightCol): ...
   ```
   
   with related `Params` and uses it to replace `JavaPredictor` and 
`HasWeightCol` in `IsotonicRegression` base classes and `JavaPredictor` in 
`IsotonicRegressionModel` base classes.
   
   ### Why are the changes needed?
   
   Previous work (#25776) on 
[SPARK-28985](https://issues.apache.org/jira/browse/SPARK-28985) replaced 
`JavaEstimator`, `HasFeaturesCol`, `HasLabelCol`, `HasPredictionCol` in 
`IsotonicRegression` and `JavaModel` in `IsotonicRegressionModel` with newly 
added `JavaPredictor`:
   
   
https://github.com/apache/spark/blob/e97b55d32285052a1f76cca35377c4b21eb2e7d7/python/pyspark/ml/wrapper.py#L377
   
   and `JavaPredictionModel`
   
   
https://github.com/apache/spark/blob/e97b55d32285052a1f76cca35377c4b21eb2e7d7/python/pyspark/ml/wrapper.py#L405
   
   respectively.
   
   This however is inconsistent with Scala counterpart where both  classes 
extend private `IsotonicRegressionBase`
   
   
https://github.com/apache/spark/blob/3cb1b57809d0b4a93223669f5c10cea8fc53eff6/mllib/src/main/scala/org/apache/spark/ml/regression/IsotonicRegression.scala#L42-L43
   
   This preserves some of the existing inconsistencies (`model` as defined in 
[the official 
example](https://github.com/apache/spark/blob/master/examples/src/main/python/ml/isotonic_regression_example.py)),
 i.e.
   
   ```python
   from pyspark.ml.regression impor IsotonicRegressionMode
   from pyspark.ml.param.shared import HasWeightCol
   
   issubclass(IsotonicRegressionModel, HasWeightCol) 
   # False
   
   hasattr(model, "weightCol")                                                  
     
   # True
   ```
   
   as well as introduces a bug, by adding unsupported `predict` method:
   
   ```python
   import inspect
   
   hasattr(model, "predict")                                                    
     
   # True
   
   inspect.getfullargspec(IsotonicRegressionModel.predict)                      
     
   # FullArgSpec(args=['self', 'value'], varargs=None, varkw=None, 
defaults=None, kwonlyargs=[], kwonlydefaults=None, annotations={})
   
   IsotonicRegressionModel.predict.__doc__                                      
                                                                                
                                     
   # Predict label for the given features.\n\n        .. versionadded:: 3.0.0'
   
   model.predict(dataset.first().features)  
   
   # Py4JError: An error occurred while calling o49.predict. Trace:
   # py4j.Py4JException: Method predict([class 
org.apache.spark.ml.linalg.SparseVector]) does not exist
   # ...
   
   ```
   
   Furthermore existing implementation can cause further problems in the 
future, if `Predictor` / `PredictionModel` API changes.
   
   ### Does this PR introduce any user-facing change?
   
   Yes. It:
   
   - Removes invalid `IsotonicRegressionModel.predict` method.
   - Adds `HasWeightColumn` to `IsotonicRegressionModel`.
   
   however the faulty implementation hasn't been released yet, and proposed 
additions have neglegible potential for breaking existing code (and none, 
compared to changes already made in #25776).
   
   
   ### How was this patch tested?
   
   - Existing unit tests.
   - Manual testing.
   
   CC @huaxingao, @zhengruifeng

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