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[].

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

如何Guitar从因子对象中获取因子标签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"

请参阅相关帖子：将 data.frame 列从因子转换为字符

或子集级别：

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