r - ggplot 停止 geom_segment 在图例中显示 geom_boxplot

Question

我正在尝试获得类似于 Glen_b 对 this question 的回答的内容.基本上，我希望箱线图顶部有一个箭头，以指示使用 ggplot 时有更多超出比例的异常值。

我可以让情节的主要部分看起来像我想要的那样，但我在获得合理的图例时遇到了问题。

我举了一个例子:

library(plyr)
library(dplyr)
library(ggplot2)

#create test data frame with extreme outlier
mpg_test <- mpg

mpg_test[1,"hwy"] = 250
pmax = 50
pmin = min(mpg_test$hwy)

outliersabovepmax <- filter(mpg_test, hwy > pmax) %>% mutate(hwy= pmax) 

#basic plot without cropping/adding arrows
p <- ggplot(mpg_test, aes(x = class, y=hwy, colour = class)) + geom_boxplot()
p

我可以让情节的主体看起来像我想要的那样:

#plot that I want
p2 <- p + 
  geom_segment(data = outliersabovepmax, 
               aes(xend = class, y = hwy-1, yend = hwy+1, 
                   linetype = "Outlier above"), 
               arrow = arrow(), show.legend = T) +
  coord_cartesian(ylim = c(pmin, pmax))

但我希望图例不在颜色图例上显示箭头。

我通常希望能够按照以下方式做一些事情:

p2 + 
  guides(colour = guide_legend(override.aes = list(linetype = "blank")))

但是因为箱线图也使用了线型，如果我这样做，我最终会得到黑色方 block 。我也不想为 geom_segment 设置 show.legend = F，因为我想在图例中添加箭头。

作为奖励，我希望将图例中的箭头旋转为面朝上。但这并不重要。

我得到的图:

我想要的情节(用油漆制作):

Answer 1

也许是这样的？

p + 
  # hide legend in actual segment layer
  geom_segment(data = outliersabovepmax, 
               aes(xend = class, y = hwy-1, yend = hwy+1), 
               arrow = arrow(), show.legend = F)+

  # have invisible segment layer that shows legend
  geom_segment(data = outliersabovepmax, 
               aes(xend = class, y = hwy-1, yend = hwy+1, linetype = "Outlier above"), 
               arrow = arrow(), alpha = 0, show.legend = T) +

  # override alpha for linetype legend
  guides(linetype = guide_legend(override.aes = list(alpha = 1))) +

  coord_cartesian(ylim = c(pmin, pmax))

如果你想改变geom_segment的图例键的布局，你可以深入了解GeomSegment的底层代码:

library(grid)
GeomSegment2 <- ggproto("GeomSegment2", GeomSegment,
                        draw_key = function (data, params, size)                         {
                          data$linetype[is.na(data$linetype)] <- 0
                          segmentsGrob(
                            # vertical instead of horizontal line
                            0.5, 0.1, 0.5, 0.9, #0.1, 0.5, 0.9, 0.5, 
                            gp = gpar(col = alpha(data$colour, data$alpha), 
                                      lwd = data$size * .pt, 
                                      lty = data$linetype, 
                                      lineend = "butt"), 
                            arrow = params$arrow)
                        })
geom_segment2 <- function (mapping = NULL, data = NULL, stat = "identity", 
                           position = "identity", ..., arrow = NULL, arrow.fill = NULL, 
                           lineend = "butt", linejoin = "round", na.rm = FALSE, 
                           show.legend = NA, inherit.aes = TRUE) {
  layer(data = data, mapping = mapping, stat = stat, geom = GeomSegment2, 
        position = position, show.legend = show.legend, inherit.aes = inherit.aes, 
        params = list(arrow = arrow, arrow.fill = arrow.fill, 
                      lineend = lineend, linejoin = linejoin, na.rm = na.rm, 
                      ...))
}

用法:

p + 
  # hide legend in actual segment layer
  geom_segment(data = outliersabovepmax, 
               aes(xend = class, y = hwy-1, yend = hwy+1), 
               arrow = arrow(), show.legend = F)+

  # have invisible segment layer that shows legend
  geom_segment2(data = outliersabovepmax, 
               aes(xend = class, y = hwy-1, yend = hwy+1, linetype = "Outlier above"), 
               arrow = arrow(), alpha = 0, show.legend = T) +

  # override alpha for linetype legend
  guides(linetype = guide_legend(override.aes = list(alpha = 1))) +

  coord_cartesian(ylim = c(pmin, pmax))