[SPARK-4256] Define precision as 1.0 when there are no positive examples; update code formatting per pull request comments

Author: Andrew Bullen

mllib/src/main/scala/org/apache/spark/mllib/evaluation/binary/BinaryClassificationMetricComputers.scala

@@ -24,38 +24,43 @@ private[evaluation] trait BinaryClassificationMetricComputer extends Serializabl
   def apply(c: BinaryConfusionMatrix): Double
 }
 
-/** Precision. */
+/** Precision. Defined as 1.0 when there are no positive examples. */
 private[evaluation] object Precision extends BinaryClassificationMetricComputer {
-  override def apply(c: BinaryConfusionMatrix): Double =
-    if (c.numTruePositives + c.numFalsePositives == 0) {
-      0.0
+  override def apply(c: BinaryConfusionMatrix): Double = {
+    val totalPositives = c.numTruePositives + c.numFalsePositives
+    if (totalPositives == 0) {
+      1.0
     } else {
-      c.numTruePositives.toDouble / (c.numTruePositives + c.numFalsePositives)
+      c.numTruePositives.toDouble / totalPositives
     }
+  }
 }
 
-/** False positive rate. */
+/** False positive rate. Defined as 0.0 when there are no negative examples. */
 private[evaluation] object FalsePositiveRate extends BinaryClassificationMetricComputer {
-  override def apply(c: BinaryConfusionMatrix): Double =
+  override def apply(c: BinaryConfusionMatrix): Double = {
     if (c.numNegatives == 0) {
       0.0
     } else {
       c.numFalsePositives.toDouble / c.numNegatives
     }
+  }
 }
 
-/** Recall. */
+/** Recall. Defined as 0.0 when there are no positive examples. */
 private[evaluation] object Recall extends BinaryClassificationMetricComputer {
-  override def apply(c: BinaryConfusionMatrix): Double =
+  override def apply(c: BinaryConfusionMatrix): Double = {
     if (c.numPositives == 0) {
       0.0
     } else {
       c.numTruePositives.toDouble / c.numPositives
     }
+  }
 }
 
 /**
- * F-Measure.
+ * F-Measure. Defined as 0 if both precision and recall are 0. EG in the case that all examples
+ * are false positives.
  * @param beta the beta constant in F-Measure
  * @see http://en.wikipedia.org/wiki/F1_score
  */

mllib/src/test/scala/org/apache/spark/mllib/evaluation/BinaryClassificationMetricsSuite.scala

@@ -61,7 +61,7 @@ class BinaryClassificationMetricsSuite extends FunSuite with LocalSparkContext {
   }
 
   test("binary evaluation metrics for All Positive RDD") {
-    val scoreAndLabels = sc.parallelize(Seq((0.5, 1.0)), 2)
+    val scoreAndLabels = sc.parallelize(Seq((0.5, 1.0), (0.5, 1.0)), 2)
     val metrics: BinaryClassificationMetrics = new BinaryClassificationMetrics(scoreAndLabels)
 
     val threshold = Seq(0.5)
@@ -86,7 +86,7 @@ class BinaryClassificationMetricsSuite extends FunSuite with LocalSparkContext {
   }
 
   test("binary evaluation metrics for All Negative RDD") {
-    val scoreAndLabels = sc.parallelize(Seq((0.5, 0.0)), 2)
+    val scoreAndLabels = sc.parallelize(Seq((0.5, 0.0), (0.5, 0.0)), 2)
     val metrics: BinaryClassificationMetrics = new BinaryClassificationMetrics(scoreAndLabels)
 
     val threshold = Seq(0.5)
@@ -97,11 +97,11 @@ class BinaryClassificationMetricsSuite extends FunSuite with LocalSparkContext {
     val pr = recall.zip(precision)
     val prCurve = Seq((0.0, 1.0)) ++ pr
     val f1 = pr.map {
-      case (0,0) => 0.0
+      case (0, 0) => 0.0
       case (r, p) => 2.0 * (p * r) / (p + r)
     }
     val f2 = pr.map {
-      case (0,0) => 0.0
+      case (0, 0) => 0.0
       case (r, p) => 5.0 * (p * r) / (4.0 * p + r)
     }