do not persist before calling binary classification metrics

Author: mengxr

mllib/src/main/scala/org/apache/spark/ml/Model.scala

@@ -31,7 +31,7 @@ abstract class Model[M <: Model[M]] extends Transformer {
   val parent: Estimator[M]
 
   /**
-   * Fitting parameters, such that parent.fit(..., trainingParamMap) could reproduce the model.
+   * Fitting parameters, such that parent.fit(..., fittingParamMap) could reproduce the model.
    */
   val fittingParamMap: ParamMap
 }

mllib/src/main/scala/org/apache/spark/ml/evaluation/BinaryClassificationEvaluator.scala

@@ -53,7 +53,7 @@ class BinaryClassificationEvaluator extends Evaluator with Params
     val scoreAndLabels = dataset.select(map(scoreCol).attr, map(labelCol).attr)
       .map { case Row(score: Double, label: Double) =>
         (score, label)
-      }.persist(StorageLevel.MEMORY_AND_DISK)
+      }
     val metrics = new BinaryClassificationMetrics(scoreAndLabels)
     val metric = map(metricName) match {
       case "areaUnderROC" =>
@@ -63,7 +63,7 @@ class BinaryClassificationEvaluator extends Evaluator with Params
       case other =>
         throw new IllegalArgumentException(s"Do not support metric $other.")
     }
-    scoreAndLabels.unpersist()
+    metrics.unpersist()
     metric
   }
 }

mllib/src/main/scala/org/apache/spark/ml/tuning/ParamGridBuilder.scala

@@ -23,7 +23,7 @@ import scala.collection.mutable
 import org.apache.spark.ml.param._
 
 /**
- * Builder for a param grid used in grid search.
+ * Builder for a param grid used in grid search-based model selection.
  */
 class ParamGridBuilder {