R语言自学笔记：factor基础

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