[SPARK-6726][ML] Import/export for spark.ml LogisticRegressionModel

This PR adds model save/load for spark.ml's LogisticRegressionModel.  It also does minor refactoring of the default save/load classes to reuse code.

CC: mengxr

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #9606 from jkbradley/logreg-io2.

2 files changed, 18 insertions, 3 deletions

diff --git a/mllib/src/test/scala/org/apache/spark/ml/classification/LogisticRegressionSuite.scala b/mllib/src/test/scala/org/apache/spark/ml/classification/LogisticRegressionSuite.scala
index 325faf37e8..51b06b7eb6 100644
--- a/mllib/src/test/scala/org/apache/spark/ml/classification/LogisticRegressionSuite.scala
+++ b/mllib/src/test/scala/org/apache/spark/ml/classification/LogisticRegressionSuite.scala
@@ -23,7 +23,7 @@ import scala.util.Random
 import org.apache.spark.SparkFunSuite
 import org.apache.spark.ml.feature.Instance
 import org.apache.spark.ml.param.ParamsSuite
-import org.apache.spark.ml.util.MLTestingUtils
+import org.apache.spark.ml.util.{Identifiable, DefaultReadWriteTest, MLTestingUtils}
 import org.apache.spark.mllib.classification.LogisticRegressionSuite._
 import org.apache.spark.mllib.linalg.{Vector, Vectors}
 import org.apache.spark.mllib.regression.LabeledPoint
@@ -31,7 +31,8 @@ import org.apache.spark.mllib.util.MLlibTestSparkContext
 import org.apache.spark.mllib.util.TestingUtils._
 import org.apache.spark.sql.{DataFrame, Row}
 
-class LogisticRegressionSuite extends SparkFunSuite with MLlibTestSparkContext {
+class LogisticRegressionSuite
+  extends SparkFunSuite with MLlibTestSparkContext with DefaultReadWriteTest {
 
   @transient var dataset: DataFrame = _
   @transient var binaryDataset: DataFrame = _
@@ -869,6 +870,18 @@ class LogisticRegressionSuite extends SparkFunSuite with MLlibTestSparkContext {
     assert(model1a0.intercept !~= model1a1.intercept absTol 1E-3)
     assert(model1a0.coefficients ~== model1b.coefficients absTol 1E-3)
     assert(model1a0.intercept ~== model1b.intercept absTol 1E-3)
+  }
 
+  test("read/write") {
+    // Set some Params to make sure set Params are serialized.
+    val lr = new LogisticRegression()
+      .setElasticNetParam(0.1)
+      .setMaxIter(2)
+      .fit(dataset)
+    val lr2 = testDefaultReadWrite(lr)
+    assert(lr.intercept === lr2.intercept)
+    assert(lr.coefficients.toArray === lr2.coefficients.toArray)
+    assert(lr.numClasses === lr2.numClasses)
+    assert(lr.numFeatures === lr2.numFeatures)
   }
 }
diff --git a/mllib/src/test/scala/org/apache/spark/ml/util/DefaultReadWriteTest.scala b/mllib/src/test/scala/org/apache/spark/ml/util/DefaultReadWriteTest.scala
index 4545b0f281..cac4bd9aa3 100644
--- a/mllib/src/test/scala/org/apache/spark/ml/util/DefaultReadWriteTest.scala
+++ b/mllib/src/test/scala/org/apache/spark/ml/util/DefaultReadWriteTest.scala
@@ -31,8 +31,9 @@ trait DefaultReadWriteTest extends TempDirectory { self: Suite =>
    * Checks "overwrite" option and params.
    * @param instance ML instance to test saving/loading
    * @tparam T ML instance type
+   * @return  Instance loaded from file
    */
-  def testDefaultReadWrite[T <: Params with Writable](instance: T): Unit = {
+  def testDefaultReadWrite[T <: Params with Writable](instance: T): T = {
     val uid = instance.uid
     val path = new File(tempDir, uid).getPath
 
@@ -61,6 +62,7 @@ trait DefaultReadWriteTest extends TempDirectory { self: Suite =>
     val load = instance.getClass.getMethod("load", classOf[String])
     val another = load.invoke(instance, path).asInstanceOf[T]
     assert(another.uid === instance.uid)
+    another
   }
 }