r - 在 ggplot 中为美学之外的组添加 hline

Question

我有一个折线图，其中包含不同年份和月份的指标。我想为每个月添加一条中线。

library(dplyr)
library(lubridate)
library(ggplot2)

set.seed(52)

data <- tibble(
  date = seq.Date(from = as.Date("2017-01-01"), to = date("2020-12-31"), by = "month")
) %>% 
  mutate(
    metric = rnorm(n(), mean = 5, sd = 2),
    month = month(date, label = TRUE),
    year = as.factor(year(date))
  )

ggplot(data, aes(x = month, y = metric, color = year, group = year)) +
  geom_line()

我尝试使用 geom_hline() 来执行此操作，但它只会为总中位数生成一条线。

ggplot(data, aes(x = month, y = metric, color = year, group = year)) +
  geom_line() +
  geom_hline(aes(yintercept = median(metric), group = month))

^{由 reprex package 创建于 2021-11-18 (v2.0.1)}

为每个月创建中值线的最简单方法是什么？像这样:

Answer 1

这是您正在寻找的...吗？

ggplot(data, aes(x = month, y = metric, color = year, group = year)) +
     geom_line() +
     geom_tile(data = function(df) df %>% group_by(month) %>% 
                                          summarise(metric = median(metric)),
               aes(x = month, y = metric), height = 0.05, inherit.aes = FALSE)

或者，感谢@user20650 下面的评论，这也有效...

ggplot(data, aes(x = month, y = metric, color = year, group = year)) +
     geom_line() +
     stat_summary(aes(x = month, y = metric), 
                  fun = median, 
                  geom = "tile", 
                  height = 0.05, 
                  inherit.aes = FALSE)