#因子：分类数据
#有序和无序
#整数向量+标签label
#Male/Female
#常用于lm(),glm()
> x <- factor(c("female","female","female","male"))
> y <- factor(c("female","female","female","male"),levels=c("male","female"))
> #table 对于当前的因子有一个整体的了解
> table(x)
x
female male
3 1
> #去掉因子的属性，看因子的内容
> unclass(x)
[1] 1 1 1 2
attr(,"levels")
[1] "female" "male"
> unclass(y)
[1] 2 2 2 1
attr(,"levels")
[1] "male" "female"
> class(x)#仍是因子类型
[1] "factor"
> class(y)
[1] "factor"
> class(unclass(x))#去掉因子的属性，因子变为了整型
[1] "integer"
> class(unclass(y))
[1] "integer"