[GitHub] [spark] srowen commented on a change in pull request #23881: [SPARK-26981][MLlib] Add 'Recall_at_k' metric to RankingMetrics

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srowen commented on a change in pull request #23881: [SPARK-26981][MLlib] Add 'Recall_at_k' metric to RankingMetrics
URL: https://github.com/apache/spark/pull/23881#discussion_r262056984
 
 

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 File path: mllib/src/main/scala/org/apache/spark/mllib/evaluation/RankingMetrics.scala
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 @@ -157,6 +141,63 @@ class RankingMetrics[T: ClassTag](predictionAndLabels: RDD[(Array[T], Array[T])]
     }.mean()
   }
 
+  /**
+   * Compute the average recall of all the queries, truncated at ranking position k.
+   *
+   * If for a query, the ranking algorithm returns n results, the recall value will be
 
 Review comment:
   This is fine; you could also just references the documentation for precisionAt here rather than repeat it.

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