Github user hirakendu commented on a diff in the pull request:
https://github.com/apache/spark/pull/79#discussion_r11229187
--- Diff: mllib/src/main/scala/org/apache/spark/mllib/tree/model/Node.scala
---
@@ -0,0 +1,90 @@
+/*
+ * 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
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+ */
+
+package org.apache.spark.mllib.tree.model
+
+import org.apache.spark.Logging
+import org.apache.spark.mllib.tree.configuration.FeatureType._
+
+/**
+ * Node in a decision tree
+ * @param id integer node id
+ * @param predict predicted value at the node
+ * @param isLeaf whether the leaf is a node
+ * @param split split to calculate left and right nodes
+ * @param leftNode left child
+ * @param rightNode right child
+ * @param stats information gain stats
+ */
+class Node (
--- End diff --
`Node` should be a recursive/linked structure with references to child
nodes and parent node (the latter allows for easy traversal), so I don't see
the need for `nodes: Array[Node]` as the model and the `build` method in
`Node`. The `DecisionTreeModel` should essentially be the root `Node` with
methods like `predict` etc. involving a recursive traversal on child nodes.
The method `predictIfleaf` in `Node` should be renamed to simply `predict`.
It predicts regardless of whether it's a leaf and does recursive traversal
until it hits a leaf child. The prediction value should be renamed to
`prediction` instead of `predict`, which would clean up the ambiguity with this
`predict` method.
Putting things together: `Node` should be simple with a `prediction` and
should be a recursive structure. `DecisionTreeModel` should be a wrapper around
a root `Node` member and contain methods like `predict`, `save`, `explain`,
`load` etc. based on recursive traversal.
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