ggplot2中基于“…count…”变量的“geom_label”的y值

我想创建一个柱状图,其中有一条表示平均值的垂直线和一个附在这条线上的标签,它给出了平均值的确切值。

我可以很容易地创建一个垂直线的基本直方图。

# needed library
library(ggplot2)

# mean to be used later
x_mean <- mean(x = iris$Sepal.Length, na.rm = TRUE)

# creating basic plot with line for mean
(
  plot <- ggplot(data = iris,
                 mapping = aes(x = Sepal.Length)) +
    stat_bin(
      col = "black",
      alpha = 0.7,
      na.rm = TRUE,
      mapping = aes(y = ..count..,
                    fill = ..count..)
    )  +
    geom_vline(
      xintercept = x_mean,
      linetype = "dashed",
      color = "red",
      na.rm = TRUE
    ) +
    scale_fill_gradient(name = "count",
                        low = "white",
                        high = "white") +
    guides(fill = FALSE)
)
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.

现在,我可以使用以下代码向此行添加标签:

# adding label to the line
plot +
  geom_label(mapping = aes(
    label = list(bquote("mean" == ~ .(
      format(round(x_mean, 2), nsmall = 2)
    ))),
    x = x_mean,
    y = 5  # how to automate this value choice?
  ),
  parse = TRUE)
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.

现在的问题是我正在硬编码 y -价值 geom_label ( y = 5 ). 这并不理想,因为如果我更改数据、变量或binwidth, y=5 将不再是y轴的(近似)中间。我试着设置 y = max(..count..)/2 ,但这会导致以下错误:

趣味错误(X[[i]],…):未找到对象“count”

总而言之: 如何选择 是的 价值 几何标签 在这种情况下是自动的,所以不管计数范围如何,标签总是在Y轴的中间?