本文首发于知乎专栏：https://zhuanlan.zhihu.com/p/60101041

也同步更新于我的个人博客：https://www.cnblogs.com/nickwu/p/12537049.html

2.因子/因素（Factor）

2.1 创建一个Factor

g <- c('f','m','m','m','f','m','f','m','f','f')
g <- factor(g)
#输出：f m m m f m f m f f
      Levels: f m
other_g <- factor(c('m','m','m','m','m'),levels=c('f','m'))
other_g
#输出：m m m m m
      Levels: f mgl(2,5,labels=c('female','male'))     #产生2个水平，每个水平5次，水平标签分别为female和male
#输出：female female female female female male   male   male   male   male  Levels: female male

2.2 Factor的基本操作

用table（）统计各水平的个数

g <- c('f','m','m','m','f','m','f','m','f','f')
g <- factor(g)
table(g)
#输出：g
      f m
      5 5