机器学习的特征选择(feature selection)

写在开头:刚开始接触机器学习,选择了周志华教授的《机器学习》作为入门教材,很不错的书籍,受益良多。没有使用matlab去编写代码,而是选择了使用python的scikit-learn的开发包,大致看了一下开发包的特征选择方法,结合周志华教授的书,想先总结总结feature selection的方法

特征选择

filter(过滤式)

思路

通过评估自变量与目标变量之间的关联,也就是量化两者之间的关系,我们暂且叫做量化值为“相关统计量”,然后根据相关统计量,找出相关性较强的k个自变量。

如何量化两者的关联

通常有相关系数,卡方检验,信息增益,和互信息

结合scikit-learn

1.Removing features with low variance
移除变量中变化较小的,一般用于自变量为离散型时,某个变量在n个样本中取相同的值的频率大于既定的阈值的时候,我们直接删除
2.Univariate feature selection
单变量特征选择,其中涉及到的函数最主要的两个是SelectKBest,SelectPercentile,一个选择前k个,一个选择前k%个。其中涉及到的量化方式主要有:chi2(卡方检验),f_classif,f_regression前两个用于分类,后一个用于回归。
还有几个看不懂的SelectFpr,SelectFdr,SelectFwe还没用到就没有深究。

wrapper(包裹式)

思路

直接将原始数据拿去训练,然后评估其性能,在选择其所有子集,递归着不断重复,直到最后找到性能最好的特征子集。

如何产生特征子集

Matlab中好用的数据降维和特征选择工具包 Copyright (c) 2018, Giorgio Roffo All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution * Neither the name of University of Glasgow nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值