r - 从因子中提取水平

Question

我有一个因素 instrumentF :

> instrumentF
[1] Guitar Drums  Cello  Harp  
Levels: Cello Drums Guitar Harp

假设我使用 [] 提取了该因子的一个级别.

> level2 = instrumentF[1]
> level2
[1] Guitar
Levels: Cello Drums Guitar Harp

我如何获得因子标签 Guitar来自因子对象 level2 ? level2$level似乎不起作用:

> Error in level2$level : $ operator is invalid for atomic vectors

Answer 1

转换为字符，看这个例子:

# factor variable example
instrumentF <- as.factor(c("Guitar", "Drums", "Cello", "Harp"))

instrumentF
# [1] Guitar Drums  Cello  Harp  
# Levels: Cello Drums Guitar Harp

as.character(instrumentF)[ 1 ]
# [1] "Guitar"

见相关帖子: Convert data.frame columns from factors to characters

或子集级别:

# as levels are sorted alphabetically, we need to subset the 3rd one
levels(instrumentF)[ 3 ]
# [1] "Guitar"