[SPARK-13786][ML][PYSPARK] Add save/load for pyspark.ml.tuning

## What changes were proposed in this pull request?

https://issues.apache.org/jira/browse/SPARK-13786

Add save/load for Python CrossValidator/Model and TrainValidationSplit/Model.

## How was this patch tested?

Test with Python doctest.

Author: Xusen Yin <yinxusen@gmail.com>

Closes #12020 from yinxusen/SPARK-13786.

3 files changed, 29 insertions, 0 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/param/params.scala b/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
index d7837b6730..c368aadd23 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/param/params.scala
@@ -18,6 +18,7 @@
 package org.apache.spark.ml.param
 
 import java.lang.reflect.Modifier
+import java.util.{List => JList}
 import java.util.NoSuchElementException
 
 import scala.annotation.varargs
@@ -833,6 +834,11 @@ final class ParamMap private[ml] (private val map: mutable.Map[Param[Any], Any])
     this
   }
 
+  /** Put param pairs with a [[java.util.List]] of values for Python. */
+  private[ml] def put(paramPairs: JList[ParamPair[_]]): this.type = {
+    put(paramPairs.asScala: _*)
+  }
+
   /**
    * Optionally returns the value associated with a param.
    */
@@ -932,6 +938,11 @@ final class ParamMap private[ml] (private val map: mutable.Map[Param[Any], Any])
     }
   }
 
+  /** Java-friendly method for Python API */
+  private[ml] def toList: java.util.List[ParamPair[_]] = {
+    this.toSeq.asJava
+  }
+
   /**
    * Number of param pairs in this map.
    */
diff --git a/mllib/src/main/scala/org/apache/spark/ml/tuning/CrossValidator.scala b/mllib/src/main/scala/org/apache/spark/ml/tuning/CrossValidator.scala
index 040b0093b9..4d9d4d472e 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/tuning/CrossValidator.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/tuning/CrossValidator.scala
@@ -17,6 +17,10 @@
 
 package org.apache.spark.ml.tuning
 
+import java.util.{List => JList}
+
+import scala.collection.JavaConverters._
+
 import com.github.fommil.netlib.F2jBLAS
 import org.apache.hadoop.fs.Path
 import org.json4s.DefaultFormats
@@ -200,6 +204,11 @@ class CrossValidatorModel private[ml] (
     @Since("1.5.0") val avgMetrics: Array[Double])
   extends Model[CrossValidatorModel] with CrossValidatorParams with MLWritable {
 
+  /** A Python-friendly auxiliary constructor. */
+  private[ml] def this(uid: String, bestModel: Model[_], avgMetrics: JList[Double]) = {
+    this(uid, bestModel, avgMetrics.asScala.toArray)
+  }
+
   @Since("1.4.0")
   override def transform(dataset: DataFrame): DataFrame = {
     transformSchema(dataset.schema, logging = true)
diff --git a/mllib/src/main/scala/org/apache/spark/ml/tuning/TrainValidationSplit.scala b/mllib/src/main/scala/org/apache/spark/ml/tuning/TrainValidationSplit.scala
index 07330bb6b0..0f2179c2a1 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/tuning/TrainValidationSplit.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/tuning/TrainValidationSplit.scala
@@ -17,6 +17,10 @@
 
 package org.apache.spark.ml.tuning
 
+import java.util.{List => JList}
+
+import scala.collection.JavaConverters._
+
 import org.apache.hadoop.fs.Path
 import org.json4s.DefaultFormats
 
@@ -198,6 +202,11 @@ class TrainValidationSplitModel private[ml] (
     @Since("1.5.0") val validationMetrics: Array[Double])
   extends Model[TrainValidationSplitModel] with TrainValidationSplitParams with MLWritable {
 
+  /** A Python-friendly auxiliary constructor. */
+  private[ml] def this(uid: String, bestModel: Model[_], validationMetrics: JList[Double]) = {
+    this(uid, bestModel, validationMetrics.asScala.toArray)
+  }
+
   @Since("1.5.0")
   override def transform(dataset: DataFrame): DataFrame = {
     transformSchema(dataset.schema, logging = true)