[SPARK-7585] [ML] [DOC] VectorIndexer user guide section

Added VectorIndexer section to ML user guide.  Also added javaCategoryMaps() method and Java unit test for it.

CC: mengxr

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

Closes #6255 from jkbradley/vector-indexer-guide and squashes the following commits:

dbb8c4c [Joseph K. Bradley] simplified VectorIndexerModel.javaCategoryMaps
f692084 [Joseph K. Bradley] Added VectorIndexer section to ML user guide.  Also added javaCategoryMaps() method and Java unit test for it.

2 files changed, 13 insertions, 1 deletions

diff --git a/mllib/src/main/scala/org/apache/spark/ml/feature/VectorIndexer.scala b/mllib/src/main/scala/org/apache/spark/ml/feature/VectorIndexer.scala
index 6d1d0524e5..e238fb310e 100644
--- a/mllib/src/main/scala/org/apache/spark/ml/feature/VectorIndexer.scala
+++ b/mllib/src/main/scala/org/apache/spark/ml/feature/VectorIndexer.scala
@@ -17,6 +17,11 @@
 
 package org.apache.spark.ml.feature
 
+import java.lang.{Double => JDouble, Integer => JInt}
+import java.util.{Map => JMap}
+
+import scala.collection.JavaConverters._
+
 import org.apache.spark.annotation.AlphaComponent
 import org.apache.spark.ml.{Estimator, Model}
 import org.apache.spark.ml.attribute._
@@ -248,6 +253,11 @@ class VectorIndexerModel private[ml] (
     val categoryMaps: Map[Int, Map[Double, Int]])
   extends Model[VectorIndexerModel] with VectorIndexerParams {
 
+  /** Java-friendly version of [[categoryMaps]] */
+  def javaCategoryMaps: JMap[JInt, JMap[JDouble, JInt]] = {
+    categoryMaps.mapValues(_.asJava).asJava.asInstanceOf[JMap[JInt, JMap[JDouble, JInt]]]
+  }
+
   /**
    * Pre-computed feature attributes, with some missing info.
    * In transform(), set attribute name and other info, if available.
diff --git a/mllib/src/test/java/org/apache/spark/ml/feature/JavaVectorIndexerSuite.java b/mllib/src/test/java/org/apache/spark/ml/feature/JavaVectorIndexerSuite.java
index 161100134c..c7ae5468b9 100644
--- a/mllib/src/test/java/org/apache/spark/ml/feature/JavaVectorIndexerSuite.java
+++ b/mllib/src/test/java/org/apache/spark/ml/feature/JavaVectorIndexerSuite.java
@@ -19,6 +19,7 @@ package org.apache.spark.ml.feature;
 
 import java.io.Serializable;
 import java.util.List;
+import java.util.Map;
 
 import org.junit.After;
 import org.junit.Assert;
@@ -64,7 +65,8 @@ public class JavaVectorIndexerSuite implements Serializable {
       .setMaxCategories(2);
     VectorIndexerModel model = indexer.fit(data);
     Assert.assertEquals(model.numFeatures(), 2);
-    Assert.assertEquals(model.categoryMaps().size(), 1);
+    Map<Integer, Map<Double, Integer>> categoryMaps = model.javaCategoryMaps();
+    Assert.assertEquals(categoryMaps.size(), 1);
     DataFrame indexedData = model.transform(data);
   }
 }