[GitHub] [spark] mgaido91 commented on a change in pull request #25383: [SPARK-13677][ML] Implement Tree-Based Feature Transformation for ML

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mgaido91 commented on a change in pull request #25383: [SPARK-13677][ML] Implement Tree-Based Feature Transformation for ML
URL: https://github.com/apache/spark/pull/25383#discussion_r312695424
 
 

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 File path: mllib/src/main/scala/org/apache/spark/ml/tree/treeModels.scala
 ##########
 @@ -78,6 +78,28 @@ private[spark] trait DecisionTreeModel {
 
   /** Convert to spark.mllib DecisionTreeModel (losing some information) */
   private[spark] def toOld: OldDecisionTreeModel
+
+  /** Returns an iterator that traverses (DFS, left to right) the leaves
+   *  in the subtree of this node.
+   */
+  private def leafIterator(node: Node): Iterator[LeafNode] = {
+    node match {
+      case l: LeafNode => Iterator.single(l)
+      case n: InternalNode =>
+        leafIterator(n.leftChild) ++ leafIterator(n.rightChild)
+    }
+  }
+
+  @transient private lazy val leafIndices: Map[LeafNode, Int] = {
 
 Review comment:
   I am a bit worried by the extra memory pressure caused by this, in case trees are big.... can't we rather assign an index to the `LeafNode` class?

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