April 2019
Intermediate to advanced
172 pages
4h 39m
Chinese
Content preview from 精通特征工程
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.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.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.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.
简单而又奇妙的数值
｜
5
果特征是某种累计值，那么它最终可能会超出训练树的取值范围。如果出现了这种情况，
就必须定期地对输入尺度进行调整；另外一种解决方案是使用区间计数方法，我们将
在第
5
章中介绍。
数值型特征的分布也非常重要，这种分布可以表示出一个特定值出现的概率。输入特征的
分布对于某些模型来说比其他模型更重要。例如，线性回归模型的训练过程需要假定预
测误差近似地服从高斯分布。这种假定通常是没有问题的，除了预测目标分布在多个数
量级中的时候，在这种情况下，误差符合高斯分布的假定将不会被满足。一种解决方法
是对输出目标进行转换，以消除数量级带来的影响。（严格说来，这应该称为目标工程，
而不是特征工程。）对数变换（
指数变换
的一种特殊形式）可以使变量的分布更加接近于
高斯分布。
除了对特征进行转换以满足模型或训练过程中的假设，还可以将多个特征组合在一起形成
更复杂的特征。我们希望复杂特征能更加简洁地捕获到原始数据中的重要信息。使输入特
征“更具信息量”可以使模型本身更简单，更容易训练和评价，也能做出更好的预测。极
端情况下，我们可以使用统计模型的输出作为复杂特征，这种思想称为
模型堆叠
，我们将
在第
7
章和第
8
章中详细介绍。本章只给出一个最简单的复杂特征示例：
交互特征
。
交互特征的构造非常简单，但将特征组合输入到模型中后，会产生各种各样的结果。为了
降低计算成本，通常需要使用自动的
特征选择
技术对输入特征进行精简。
我们先介绍一些基本概念：标量、向量和空间，然后讨论特征尺度、特征分布、交互特征
和特征选择。
2.1
标量 ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
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.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
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.