[SPARK-9847] [ML] Modified copyValues to distinguish between default, explicit param values

mllib/src/main/scala/org/apache/spark/ml/param/params.scala

@@ -559,13 +559,26 @@ trait Params extends Identifiable with Serializable {
 
   /**
    * Copies param values from this instance to another instance for params shared by them.
-   * @param to the target instance
-   * @param extra extra params to be copied
+   *
+   * This handles default Params and explicitly set Params separately.
+   * Default Params are copied from and to [[defaultParamMap]], and explicitly set Params are
+   * copied from and to [[paramMap]].
+   * Warning: This implicitly assumes that this [[Params]] instance and the target instance
+   *          share the same set of default Params.
+   *
+   * @param to the target instance, which should work with the same set of default Params as this
+   *           source instance
+   * @param extra extra params to be copied to the target's [[paramMap]]
    * @return the target instance with param values copied
    */
   protected def copyValues[T <: Params](to: T, extra: ParamMap = ParamMap.empty): T = {
-    val map = extractParamMap(extra)
+    val map = paramMap ++ extra
     params.foreach { param =>
+      // copy default Params
+      if (defaultParamMap.contains(param) && to.hasParam(param.name)) {
+        to.defaultParamMap.put(to.getParam(param.name), defaultParamMap(param))
+      }
+      // copy explicitly set Params
       if (map.contains(param) && to.hasParam(param.name)) {
         to.set(param.name, map(param))
       }

mllib/src/test/scala/org/apache/spark/ml/param/ParamsSuite.scala

@@ -200,6 +200,14 @@ class ParamsSuite extends SparkFunSuite {
     val inArray = ParamValidators.inArray[Int](Array(1, 2))
     assert(inArray(1) && inArray(2) && !inArray(0))
   }
+
+  test("Params.copyValues") {
+    val t = new TestParams()
+    val t2 = t.copy(ParamMap.empty)
+    assert(!t2.isSet(t2.maxIter))
+    val t3 = t.copy(ParamMap(t.maxIter -> 20))
+    assert(t3.isSet(t3.maxIter))
+  }
 }
 
 object ParamsSuite extends SparkFunSuite {