#因子：分類資料
#有序和無序
#整數向量+標籤label
#Male/Female
#常用於lm(),glm()

> x <- factor(c("female","female","female","male"))
> y <- factor(c("female","female","female","male"),levels=c("male","female"))

> #table 對於當前的因子有一個整體的瞭解
> table(x)
x
female male
3 1

> #去掉因子的屬性，看因子的內容
> 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)#仍是因子型別
[1] "factor"

> class(y)
[1] "factor"

> class(unclass(x))#去掉因子的屬性，因子變為了整型
[1] "integer"

> class(unclass(y))
[1] "integer"