How to extract best parameters from a CrossValidat

Question

I want to find the parameters of ParamGridBuilder that make the best model in CrossValidator in Spark 1.4.x,

In Pipeline Example in Spark documentation, they add different parameters (numFeatures, regParam) by using ParamGridBuilder in the Pipeline. Then by the following line of code they make the best model:

val cvModel = crossval.fit(training.toDF)

Now, I want to know what are the parameters (numFeatures, regParam) from ParamGridBuilder that produces the best model.

I already used the following commands without success:

cvModel.bestModel.extractParamMap().toString()
cvModel.params.toList.mkString("(", ",", ")")
cvModel.estimatorParamMaps.toString()
cvModel.explainParams()
cvModel.getEstimatorParamMaps.mkString("(", ",", ")")
cvModel.toString()

Any help?

Thanks in advance,

Answer 1

this java code should work: cvModel.bestModel().parent().extractParamMap().you can translate it to scala code parent()method will return an estimator, you can get the best params then.

Answer 2

One method to get a proper ParamMap object is to use CrossValidatorModel.avgMetrics: Array[Double] to find the argmax ParamMap:

implicit class BestParamMapCrossValidatorModel(cvModel: CrossValidatorModel) {
  def bestEstimatorParamMap: ParamMap = {
    cvModel.getEstimatorParamMaps
           .zip(cvModel.avgMetrics)
           .maxBy(_._2)
           ._1
  }
}

When run on the CrossValidatorModel trained in the Pipeline Example you cited gives:

scala> println(cvModel.bestEstimatorParamMap)
{
   hashingTF_2b0b8ccaeeec-numFeatures: 100,
   logreg_950a13184247-regParam: 0.1
}

Answer 3

To print everything in paramMap, you actually don't have to call parent:

cvModel.bestModel().extractParamMap()

To answer OP's question, to get a single best parameter, for example regParam:

cvModel.bestModel().extractParamMap().apply(cvModel.bestModel.getParam("regParam"))

Answer 4

This is how you get the chosen parameters

println(cvModel.bestModel.getMaxIter)   
println(cvModel.bestModel.getRegParam)  

Answer 5

If java，see this debug show;

bestModel.parent().extractParamMap()

Answer 6

Building in the solution of @macfeliga, a single liner that works for pipelines:

cvModel.bestModel.asInstanceOf[PipelineModel]
    .stages.foreach(stage => println(stage.extractParamMap))