理解R Factor(因子)

因子型（factor）表示编号或登记，是用来存储类别的数据类型，是离散的，与连续性值相对。如果把数字作为因子，那么在导入数据后，需要将向量转换为因子(factor)，而因子在整个计算过程中不再作为数值，而是作为“符号”。 讲的很好的R因子：https://blog.csdn.net/hsdcc217/article/details/78510087

data <- c(1,2,2,3,1,2,3,3,1,2,3,3,1)
data
fdata<-factor(data)
fdata
class(fdata)
class(data)
levels(fdata)
rdata<-factor(data,labels = c("I","II","III"))
rdata
# rdata<-factor(data.labels=c("e","ee","eee")) comma bug
rdata<-factor(data,labels=c("e","ee","eee"))
rdata
mons <- c("March","April","January","November","January", "September","October","September","November","August", "January","November","November","February","May","August", "July","December","August","August","September","November", "February","April")
mons<-factor(mons)
mons
mons = factor(mons,levels=c("January","February","March","April","May","June","July","August","September","October","November","December"),ordered=TRUE)
mons
table(mons)
?table()

　　

 

 #factor()函数将原来的数值型的向量转化为factor类型。factor类型的向量有levels的概念。Levels就是factor所有因素的集合（没有重复），Levels就是factor中元素排除重复后字符化的结果，levels元素都是character类型，可以在生成factor时，指定levels。

factor最大的作用是指定数据的顺序，即指定后边作图过程自变量的显示顺序。

Ref2:

因子水平(Level)表示因子的值域。因子的每个元素只能取因子水平中的值或缺失。

创建因子用factor()函数创建因子型变量。factor(x=character(),levels,lables=levels,

 还可以通过factor()修改level