[SPARK-9715] [ML] Store numFeatures in all ML PredictionModel types

All prediction models should store `numFeatures` indicating the number of features the model was trained on. Default value of -1 added for backwards compatibility.

Author: sethah <seth.hendrickson16@gmail.com>

Closes #8675 from sethah/SPARK-9715.

2 files changed, 8 insertions, 0 deletions

diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaDeveloperApiExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaDeveloperApiExample.java
index a377694507..0b4c0d9ba9 100644
--- a/examples/src/main/java/org/apache/spark/examples/ml/JavaDeveloperApiExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaDeveloperApiExample.java
@@ -220,6 +220,11 @@ class MyJavaLogisticRegressionModel
   public int numClasses() { return 2; }
 
   /**
+   * Number of features the model was trained on.
+   */
+  public int numFeatures() { return weights_.size(); }
+
+  /**
    * Create a copy of the model.
    * The copy is shallow, except for the embedded paramMap, which gets a deep copy.
    * <p>
diff --git a/examples/src/main/scala/org/apache/spark/examples/ml/DeveloperApiExample.scala b/examples/src/main/scala/org/apache/spark/examples/ml/DeveloperApiExample.scala
index 340c3559b1..3758edc561 100644
--- a/examples/src/main/scala/org/apache/spark/examples/ml/DeveloperApiExample.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/ml/DeveloperApiExample.scala
@@ -172,6 +172,9 @@ private class MyLogisticRegressionModel(
   /** Number of classes the label can take.  2 indicates binary classification. */
   override val numClasses: Int = 2
 
+  /** Number of features the model was trained on. */
+  override val numFeatures: Int = weights.size
+
   /**
    * Create a copy of the model.
    * The copy is shallow, except for the embedded paramMap, which gets a deep copy.