SPARK-3278 Isotonic regression java api

Author: zapletal-martin

mllib/src/main/scala/org/apache/spark/mllib/regression/IsotonicRegression.scala

@@ -46,8 +46,8 @@ class IsotonicRegressionModel (
    * @param testData features to be labeled
    * @return predicted labels
    */
-  def predict(testData: JavaRDD[java.lang.Double]): RDD[java.lang.Double] =
-    testData.rdd.map(x => x.doubleValue()).map(predict)
+  def predict(testData: JavaRDD[java.lang.Double]): JavaRDD[java.lang.Double] =
+    testData.rdd.map(_.doubleValue()).map(predict).map(new java.lang.Double(_))
 
   /**
    * Predict a single label

mllib/src/main/scala/org/apache/spark/mllib/util/IsotonicDataGenerator.scala

@@ -21,20 +21,28 @@ import org.apache.spark.annotation.DeveloperApi
 import scala.collection.JavaConversions._
 import java.lang.{Double => JDouble}
 
+/**
+ * :: DeveloperApi ::
+ * Generate test data for Isotonic regresision.
+ */
 @DeveloperApi
 object IsotonicDataGenerator {
 
   /**
    * Return a Java List of ordered labeled points
+   *
    * @param labels list of labels for the data points
    * @return Java List of input.
    */
   def generateIsotonicInputAsList(labels: Array[Double]): java.util.List[(JDouble, JDouble)] = {
-    seqAsJavaList(generateIsotonicInput(wrapDoubleArray(labels):_*).map(x => (new JDouble(x._1), new JDouble(x._2))))
+    seqAsJavaList(
+      generateIsotonicInput(
+        wrapDoubleArray(labels):_*).map(x => (new JDouble(x._1), new JDouble(x._2))))
   }
 
   /**
    * Return an ordered sequence of labeled data points with default weights
+   *
    * @param labels list of labels for the data points
    * @return sequence of data points
    */
@@ -45,6 +53,7 @@ object IsotonicDataGenerator {
 
   /**
    * Return an ordered sequence of labeled weighted data points
+   *
    * @param labels list of labels for the data points
    * @param weights list of weights for the data points
    * @return sequence of data points

mllib/src/test/java/org/apache/spark/mllib/regression/JavaIsotonicRegressionSuite.java

@@ -86,10 +86,10 @@ public Double call(Tuple2<Double, Double> v) throws Exception {
       }
     });
 
-    Double[] predictions = model.predict(testRDD).collect();
+    List<Double> predictions = model.predict(testRDD).collect();
 
-    Assert.assertTrue(predictions[0] == 1d);
-    Assert.assertTrue(predictions[11] == 12d);
+    Assert.assertTrue(predictions.get(0) == 1d);
+    Assert.assertTrue(predictions.get(11) == 12d);
   }
 }