组合特征较多时候是用在推荐系统或者CTR预估中，下面几篇博客大概讲解了其使用，但是并没有细化每步的具体实现。
https://www.qcloud.com/community/article/701728
http://www.jianshu.com/p/7445a7b94b45
https://www.zhihu.com/question/31989952/answer/54184582 https://www.zhihu.com/question/34819617/answer/59967750
https://www.zhihu.com/question/28641663
http://www.360doc.com/content/16/0904/11/28378250_588303798.shtml
http://blog.csdn.net/big_talent/article/details/53887238
