[GitHub] [spark] zhengruifeng commented on a change in pull request #24717: [SPARK-27847][ML] One-Pass MultilabelMetrics & MulticlassMetrics

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zhengruifeng commented on a change in pull request #24717: [SPARK-27847][ML] One-Pass MultilabelMetrics & MulticlassMetrics
URL: https://github.com/apache/spark/pull/24717#discussion_r287912065
 
 

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 File path: mllib/src/main/scala/org/apache/spark/mllib/evaluation/MultilabelMetrics.scala
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 @@ -38,76 +40,62 @@ class MultilabelMetrics @Since("1.2.0") (predictionAndLabels: RDD[(Array[Double]
       (r.getSeq[Double](0).toArray, r.getSeq[Double](1).toArray)
     })
 
-  private lazy val numDocs: Long = predictionAndLabels.count()
+  /**
+   * Use MultilabelSummarizer to calculate all summary statistics of predictions
+   * and labels on one pass.
+   */
+  private lazy val summary: MultilabelSummary = {
+    predictionAndLabels
+      .treeAggregate(new MultilabelSummarizer)(
+        (summary, sample) => summary.add(sample._1, sample._2),
 
 Review comment:
   If I convert this to `(summary, (preds, l)) => summary.add(preds, l),` then the IDEA complains 

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