留坑
方差过滤
通过方差过滤来筛选无用特征
https://blog.csdn.net/fontthrone/article/details/78997449
https://www.cnblogs.com/jasonfreak/p/5448385.html
https://www.cnblogs.com/jasonfreak/p/5619260.html
https://www.cnblogs.com/learninglife/p/9340636.html