<p> 周末无事，从这一篇开始，总结几个月来学习机器学习算法的收获体会，以后争取每周更新一篇，每一篇介绍一个算法。<span class="token lf" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;background-color:rgb(241,241,241);"></span><span class="token p" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;background-color:rgb(241,241,241);">决策树是我学习的第一个机器学习算法，对于一个菜鸟而言，如此直观的二叉树形结构，想来比较好学，然而事实并非如此，磕磕绊绊总算还是学下来了，现在总结一下！</span><span class="token lf" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;background-color:rgb(241,241,241);"></span><span class="token lf" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;background-color:rgb(241,241,241);"></span><span class="token li" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;background-color:rgb(241,241,241);"><span class="token md md-li" style="color:rgba(128,128,128,.6);"> </span></span><span class="token p" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;background-color:rgb(241,241,241);"></span></p>
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<p><span style="font-weight:bold;"><span style="font-size:18px;"><span style="background-color:rgb(241,241,241);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;"><span style="color:rgb(0,0,40);">1. </span></span><span style="background-color:rgb(241,241,241);color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;">决策树模型定义：</span></span><span class="token lf" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;"></span><span style="font-size:16px;background-color:rgb(241,241,241);color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;"> </span></span></p>
<p><span class="token li" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;background-color:rgb(241,241,241);"> <span style="font-size:16px;">决策树模型是一种描述对实例进行分类的树形结构，由结点和有向边组成。结点分为根结点、内部结点以及叶结点。内部结点表示一个特征或属性，叶结点表示一个类或值。决策树模型是一种监督学习模型，既可以用来做分类，也可以用来做回归（本次只讨论分类问题）；另外，决策树还是其他很多其他监督学习的算法模型的基础，如梯度提升决策树(GBDT)、随机森林等，因此还蛮重要的~<span class="token lf"></span><span class="token md md-li" style="color:rgba(128,128,128,.6);"> </span></span></span></p>
<p><strong><span style="font-size:18px;"><span style="background-color:rgb(241,241,241);color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;"> 2. 决策树模型的学习过程：</span><span class="token lf" style="color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;"></span><span style="background-color:rgb(241,241,241);color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;"> </span></span></strong></p>
<p><span style="background-color:rgb(241,241,241);color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Microsoft YaHei', Roboto, Noto, 'Helvetica Neue', sans-serif;white-space:pre-wrap;"> <span style="font-size:16px;">假设给定训练数据集</span></span></p>
<p style="text-align:center;"><span style="background-color:rgb(241,241,241);color:rgb(90,90,90);font-family:'PingFang SC', 'Hiragino Sans GB', Arial, 'Micro |
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