moved findMax to DenseVector and renamed to argmax. fixed bug for vector of length 0

Author: jkbradley

mllib/src/main/scala/org/apache/spark/ml/classification/Classifier.scala

@@ -150,5 +150,5 @@ abstract class ClassificationModel[FeaturesType, M <: ClassificationModel[Featur
    * This may be overridden to support thresholds which favor particular labels.
    * @return  predicted label
    */
-  protected def raw2prediction(rawPrediction: Vector): Double = rawPrediction.findMax
+  protected def raw2prediction(rawPrediction: Vector): Double = rawPrediction.toDense.argmax
 }

mllib/src/main/scala/org/apache/spark/ml/classification/ProbabilisticClassifier.scala

@@ -165,5 +165,5 @@ private[spark] abstract class ProbabilisticClassificationModel[
    * This may be overridden to support thresholds which favor particular labels.
    * @return  predicted label
    */
-  protected def probability2prediction(probability: Vector): Double = probability.findMax
+  protected def probability2prediction(probability: Vector): Double = probability.toDense.argmax
 }

mllib/src/main/scala/org/apache/spark/mllib/linalg/Vectors.scala

@@ -150,26 +150,6 @@ sealed trait Vector extends Serializable {
       toDense
     }
   }
-
-  /**
-   * Find the index of a maximal element.  Returns the first maximal element in case of a tie.
-   * Returns -1 if vector has length 0.
-   */
-  private[spark] def findMax: Int = {
-    if (size == 0) {
-      0
-    } else {
-      var maxIdx = 0
-      var maxValue = apply(0)
-      foreachActive { (idx, value) =>
-        if (value > maxValue) {
-          maxIdx = idx
-          maxValue = value
-        }
-      }
-      maxIdx
-    }
-  }
 }
 
 /**
@@ -607,6 +587,28 @@ class DenseVector(val values: Array[Double]) extends Vector {
     }
     new SparseVector(size, ii, vv)
   }
+
+  /**
+   * Find the index of a maximal element.  Returns the first maximal element in case of a tie.
+   * Returns -1 if vector has length 0.
+   */
+  private[spark] def argmax: Int = {
+    if (size == 0) {
+      -1
+    } else {
+      var maxIdx = 0
+      var maxValue = values(0)
+      var i = 1
+      while (i < size) {
+        if (values(i) > maxValue) {
+          maxIdx = i
+          maxValue = values(i)
+        }
+        i += 1
+      }
+      maxIdx
+    }
+  }
 }
 
 object DenseVector {