旋转箱线图图例(R，ggplot2)

Question

我正在使用以下代码。

 library(ggplot2)
 mtcars$carb <- as.factor(mtcars$carb)
 mtcars$am <- as.factor(mtcars$am)
 mtcars <- mtcars[!(mtcars$carb==6 | mtcars$carb==8),]
 ggplot(mtcars) + 
    geom_boxplot(aes(x = carb, y = mpg, fill = am), 
                 position = position_dodge(0.9)) +
 guides(fill = guide_legend(direction = "horizontal"))

这会导致:

我想旋转图例以获得所需的结果:

有人可以帮忙吗？谢谢。

Answer 1

好吧，我根据@LFischer 的建议想出了办法。可能有一种更简单的方法，但经过一番尝试和错误后，这对我来说是这样:

 library(ggplot2)
 mtcars$carb <- as.factor(mtcars$carb)
 mtcars$am <- as.factor(mtcars$am)
 mtcars <- mtcars[!(mtcars$carb==6 | mtcars$carb==8),]
 ggplot(mtcars) + 
    geom_boxplot(aes(x = carb, y = mpg, fill = am), 
                 position = position_dodge(0.9)) +
 guides(fill = guide_legend(reverse = TRUE, direction = "vertical", label.position = "top", label.theme = element_text(angle = 90, vjust = 0.5), title.position = "bottom", title.theme = element_text(angle = 90)))