一.factor的基本概念
1.创建以及修改
factor相当于一个向量,但是向量内不同的元素由称为level的标签标识,从而用不同的数值标识这些元素:
> x <- c("single", "married", "married", "single");
> str(x);
chr [1:4] "single" "married" "married" "single"
> x <- as.factor(x);
> str(x);
Factor w/ 2 levels "married","single": 2 1 1 2
若要在factor添加量,首先需要添加对应的标识levels,随后再添加factors:
levels(x) <- c("single", "married", "widowed");
x[ length(y) + 1 ] <- "widowed";
注意:在修改levels时,对于一个已经确定的factors,其对应得数值表示已经确定,再次修改levels只会在原来的“数字顺序”基础上改变标识:
mon <- c("Mar","Nov","Mar","Aug","Sep","Jun","Nov","Nov","Oct","Jun","May","Sep","Dec","Jul","Nov")
mon <- as.factor(mon)
mon
levels(mon) <- c("Jan", "Feb", "Mar", "Apr", "May","Jun","Jul", "Aug", "Sep", "Oct", "Nov", "Dec")
mon
运行结果:
[1] Mar Nov Mar Aug Sep Jun Nov Nov Oct Jun May Se