Question

这可能很简单，我觉得这很愚蠢。我想使用mutate更改数据框中因子的级别。简单的例子：

library("dplyr")
dat <- data.frame(x = factor("A"), y = 1)
mutate(dat,levels(x) = "B")

我明白了：

Error: Unexpected '=' in "mutate(dat,levels(x) ="

为什么这不起作用？如何用mutate改变因子水平？

Answer 1

使用forcats中的tidyverse包，这也很简单。

mutate(dat, x = fct_recode(x, "B" = "A"))

Answer 2

我不太确定我是否理解你的问题，但是如果你想用[{1}}更改cyl的因子级别，你可以这样做：

mutate()

你会得到：

df <- mtcars %>% mutate(cyl = factor(cyl, levels = c(4, 6, 8)))

Answer 3

也许你正在寻找这个plyr :: revalue函数：

mutate(dat, x = revalue(x, c("A" = "B")))

你也可以看到plyr :: mapvalues。

Answer 4

您可以使用recode中的dplyr功能。

df <- iris %>%
     mutate(Species = recode(Species, setosa = "SETOSA",
         versicolor = "VERSICOLOR",
         virginica = "VIRGINICA"
     )
)

Answer 5

无法评论，因为我没有足够的声望点，但重新编码仅适用于矢量，所以@ Stefano的答案中的上述代码应为

df <- iris %>%
  mutate(Species = recode(Species, 
     setosa = "SETOSA",
     versicolor = "VERSICOLOR",
     virginica = "VIRGINICA")
  )

Answer 6

根据我的理解，当前接受的答案只会改变因子级别的顺序，而不是实际的标签（即，如何调用因子的级别）。为了说明级别和标签之间的区别，请考虑以下示例：

将cyl变为系数（因为它们以字母数字顺序编码，所以不需要指定级别）：

    mtcars2 <- mtcars %>% mutate(cyl = factor(cyl, levels = c(4, 6, 8))) 
    mtcars2$cyl[1:5]
    #[1] 6 6 4 6 8
    #Levels: 4 6 8

更改级别的顺序（但不是标签本身：cyl仍然是同一列）

    mtcars3 <- mtcars2 %>% mutate(cyl = factor(cyl, levels = c(8, 6, 4))) 
    mtcars3$cyl[1:5]
    #[1] 6 6 4 6 8
    #Levels: 8 6 4
    all(mtcars3$cyl==mtcars2$cyl)
    #[1] TRUE

将新标签分配给cyl标签的顺序为：c（8,6,4），因此我们按如下方式指定新标签：

    mtcars4 <- mtcars3 %>% mutate(cyl = factor(cyl, labels = c("new_value_for_8", 
                                                               "new_value_for_6", 
                                                               "new_value_for_4" )))
    mtcars4$cyl[1:5]
    #[1] new_value_for_6 new_value_for_6 new_value_for_4 new_value_for_6 new_value_for_8
    #Levels: new_value_for_8 new_value_for_6 new_value_for_4

请注意此列与第一列的不同之处：

    all(as.character(mtcars4$cyl)!=mtcars3$cyl) 
    #[1] TRUE 
    #Note: TRUE here indicates that all values are unequal because I used != instead of ==
    #as.character() was required as the levels were numeric and thus not comparable to a character vector

更多详情：

如果我们要使用cyl而不是mtcars2来更改mtcars3的级别，我们需要以不同方式指定标签以获得相同的结果。 mtcars2的标签顺序为：c（4,6,8），因此我们指定新标签如下

    #change labels of mtcars2 (order used to be: c(4, 6, 8)
    mtcars5 <- mtcars2 %>% mutate(cyl = factor(cyl, labels = c("new_value_for_4", 
                                                               "new_value_for_6", 
                                                               "new_value_for_8" )))

与mtcars3$cyl和mtcars4$cyl不同，mtcars4$cyl和mtcars5$cyl的标签因此是相同的，即使它们的级别有不同的顺序。

    mtcars4$cyl[1:5]
    #[1] new_value_for_6 new_value_for_6 new_value_for_4 new_value_for_6 new_value_for_8
    #Levels: new_value_for_8 new_value_for_6 new_value_for_4

    mtcars5$cyl[1:5]
    #[1] new_value_for_6 new_value_for_6 new_value_for_4 new_value_for_6 new_value_for_8
    #Levels: new_value_for_4 new_value_for_6 new_value_for_8

    all(mtcars4$cyl==mtcars5$cyl)
    #[1] TRUE

    levels(mtcars4$cyl) == levels(mtcars5$cyl)
    #1] FALSE  TRUE FALSE

用dplyr mutate改变因子水平

6 个答案: