April 2019
Intermediate to advanced
172 pages
4h 39m
Chinese
Content preview from 精通特征工程
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28
｜
第
2
章
图 2-18： 原始及缩放后的新闻文章单词数量。注意只有
x
轴的尺度发生了变化，特征缩放后的分布
形状保持不变
当一组输入特征的尺度相差很大时，就需要进行特征缩放。例如，一个人气很高的商业网
站的日访问量可能是几十万次，而实际购买行为可能只有几千次。如果这两个特征都被模
型所使用，那么模型就需要在确定如何使用它们时先平衡一下尺度。如果输入特征的尺度
差别非常大，就会对模型训练算法带来数值稳定性方面的问题。在这种情况下，就应该对
特征进行标准化。第
4
章将详细介绍特征缩放在自然文本处理中的应用，并给出几个使用
示例。
2.5
交互特征
两个特征的乘积可以组成一对简单的
交互特征
，这种相乘关系可以用逻辑操作符
AND
来
类比，它可以表示出由一对条件形成的结果：“该购买行为来自于邮政编码为
98121
的地
区”
AND
“用户年龄在
18
和
35
岁之间”。这种特征在基于决策树的模型中极其常见，在
广义线性模型中也经常使用。
简单线性模型使用独立输入特征
x
1
,
x
2
,
…
,
x
n
的线性组合来预测结果变量
y
：
11 2 2 nn
y wx wx w x= + ++
简单而又奇妙的数值
｜
29
很容易对线性模型进行扩展，使之包含输入特征的两两组合，如下所示：
11 22 1,111 1,2121,3 13nn
y
wx wx
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.