在 geom_密度_脊上画线

Question

我试图在 ggridges 的密度图中画一条线

library(ggplot2)
library(ggridges)
ggplot(iris, aes(x = Sepal.Length, y = Species)) + 
  geom_density_ridges(rel_min_height = 0.01)

指示最高点并标记该点的 x 值。像下面这样的东西。非常感谢任何有关实现此目标的建议

Answer 1

一种巧妙的方法是询问 ggplot 对象本身并使用它来构造附加功能：

# This is the OP chart
library(ggplot2)
library(ggridges)
gr <- ggplot(iris, aes(x = Sepal.Length, y = Species)) + 
  geom_density_ridges(rel_min_height = 0.01)  

编辑：下一部分已被缩短，用于purrr::pluck提取列表的整个data部分，而不是手动指定我们稍后需要的列。

# Extract the data ggplot used to prepare the figure.
#   purrr::pluck is grabbing the "data" list from the list that
#   ggplot_build creates, and then extracting the first element of that list.
ingredients <- ggplot_build(gr) %>% purrr::pluck("data", 1)

# Pick the highest point. Could easily add quantiles or other features here.
density_lines <- ingredients %>%
  group_by(group) %>% filter(density == max(density)) %>% ungroup()

# Use the highest point to add more geoms
ggplot(iris, aes(x = Sepal.Length, y = Species)) + 
  geom_density_ridges(rel_min_height = 0.01) +
  geom_segment(data = density_lines, 
               aes(x = x, y = ymin, xend = x, 
                   yend = ymin+density*scale*iscale)) +
  geom_text(data = density_lines, 
            aes(x = x, y = ymin + 0.5 *(density*scale*iscale),
                label = round(x, 2)),
            hjust = -0.2)