Github user 0asa commented on a diff in the pull request: https://github.com/apache/spark/pull/2435#discussion_r19732330 --- Diff: mllib/src/main/scala/org/apache/spark/mllib/tree/impl/DecisionTreeMetadata.scala --- @@ -128,13 +139,34 @@ private[tree] object DecisionTreeMetadata { } } + // Set number of features to use per node (for random forests). + val _featureSubsetStrategy = featureSubsetStrategy match { + case "auto" => if (numTrees == 1) "all" else "sqrt" + case _ => featureSubsetStrategy + } + val numFeaturesPerNode: Int = _featureSubsetStrategy match { + case "all" => numFeatures + case "sqrt" => math.sqrt(numFeatures).ceil.toInt + case "log2" => math.max(1, (math.log(numFeatures) / math.log(2)).ceil.toInt) --- End diff -- +1 for `sqrt` as it has been widely used as a standard default for such ensemble methods.
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