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From hirakendu <...@git.apache.org>
Subject [GitHub] spark pull request: MLI-1 Decision Trees
Date Wed, 02 Apr 2014 21:36:20 GMT
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
    + * limitations under the License.
    + */
    +
    +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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