Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/5530#discussion_r28486992
--- Diff: mllib/src/main/scala/org/apache/spark/ml/impl/tree/Node.scala ---
@@ -0,0 +1,201 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ml.impl.tree
+
+import org.apache.spark.mllib.linalg.Vector
+import org.apache.spark.mllib.tree.model.{InformationGainStats =>
OldInformationGainStats,
+ Node => OldNode, Predict => OldPredict}
+
+
+/**
+ * Decision tree node interface.
+ */
+sealed trait Node extends Serializable {
+
+ // TODO: Add aggregate stats (once available). This will happen after
we move the DecisionTree
+ // code into the new API and deprecate the old API.
+
+ /** Prediction this node makes (or would make, if it is an internal
node) */
+ def prediction: Double
+
+ /** Impurity measure at this node (for training data) */
+ def impurity: Double
+
+ /** Recursive prediction helper method */
+ private[ml] def predict(features: Vector): Double = prediction
+
+ /**
+ * Get the number of nodes in tree below this node, including leaf nodes.
+ * E.g., if this is a leaf, returns 0. If both children are leaves,
returns 2.
+ */
+ private[tree] def numDescendants: Int
+
+ /**
+ * Recursive print function.
+ * @param indentFactor The number of spaces to add to each level of
indentation.
+ */
+ private[tree] def subtreeToString(indentFactor: Int = 0): String
+
+ /**
+ * Get depth of tree from this node.
+ * E.g.: Depth 0 means this is a leaf node. Depth 1 means 1 internal
and 2 leaf nodes.
+ */
+ private[tree] def subtreeDepth: Int
+
+ /**
+ * Create a copy of this node in the old Node format, recursively
creating child nodes as needed.
+ * @param id Node ID using old format IDs
+ */
+ private[ml] def toOld(id: Int): OldNode
+}
+
+private[ml] object Node {
+
+ /**
+ * Create a new Node from the old Node format, recursively creating
child nodes as needed.
+ */
+ def fromOld(oldNode: OldNode): Node = {
+ if (oldNode.isLeaf) {
+ // TODO: Once the implementation has been moved to this API, then
include sufficient
+ // statistics here.
+ new LeafNode(prediction = oldNode.predict.predict, impurity =
oldNode.impurity)
+ } else {
+ val gain = if (oldNode.stats.nonEmpty) {
+ oldNode.stats.get.gain
+ } else {
+ 0.0
+ }
+ new InternalNode(prediction = oldNode.predict.predict, impurity =
oldNode.impurity,
+ gain = gain, leftChild = fromOld(oldNode.leftNode.get),
+ rightChild = fromOld(oldNode.rightNode.get), split =
Split.fromOld(oldNode.split.get))
+ }
+ }
+
+ /**
+ * Helper method for [[Node.subtreeToString()]].
+ * @param split Split to print
+ * @param left Indicates whether this is the part of the split going to
the left,
+ * or that going to the right.
+ */
+ private[tree] def splitToString(split: Split, left: Boolean): String = {
--- End diff --
Should be `private` instead of `private[tree] since this is only called by
`subtreeToString`.
---
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