ggplot2：如何在时间 x 轴上将文本添加到多条垂直线（geom_vlines）？

Question

请看下面的例子

library(dplyr)
library(lubridate)
library(ggplot2)
data <- data_frame(time = c(ymd(20160201),
                            ymd(20160202),
                            ymd(20160203),
                            ymd(20160201),
                            ymd(20160202)),
                            value = c(1,1,1,2,2), 
                            group = c('A','A','B','B','B'))

events <- data_frame(time = c(ymd(20160201), 
                              ymd(20160202)),
                     text = c('who let the dogs out?',
                              'who? who? who?'))

ggplot(data, aes(x = time, y = value, group = group, color = group)) + 
  geom_line(size = 2 ) +
  geom_vline(data = events, aes(xintercept = as.numeric(time)))  

> data
# A tibble: 5 × 3
        time value group
      <date> <dbl> <chr>
1 2016-02-01     1     A
2 2016-02-02     1     A
3 2016-02-03     1     B
4 2016-02-01     2     B
5 2016-02-02     2     B

> events
# A tibble: 2 × 2
        time                  text
      <date>                 <chr>
1 2016-02-01 who let the dogs out?
2 2016-02-02        who? who? who?

我想为每个组（A 和 B）获取变量 value 的折线图，并在 events 数据框中每次发生事件时绘制垂直线。

使用ggplot vertical line with date axis、How to get a vertical geom_vline to an x-axis of class date? 和How to add legend for vertical lines in ggplot? 的想法我可以轻松做到：

ggplot(data, aes(x = time, y = value, group = group, color = group)) + 
  geom_line(size = 2 ) +
  geom_vline(data = events, aes(xintercept = as.numeric(time)))

问题是我想用相应的文本标记每条垂直线（每个事件），如R ggplot2: Labelling a horizontal line on the y axis with a numeric value。

很遗憾，执行以下操作不起作用

ggplot(data, aes(x = time, y = value, group = group, color = group)) + 
  geom_line(size = 2 ) +
  geom_vline(data = events, aes(xintercept = as.numeric(time)))  +
  geom_text(data = events, aes(x = as.numeric(time), y = 0, label = text))

这里有什么问题？有任何想法吗？ 谢谢！

Answer 1

你可以试试

ggplot(data, aes(x = time)) + 
  geom_line(aes(y = value, group = group, color = group), size = 2 ) +
  geom_vline(data = events, aes(xintercept = as.numeric(time)))  +
  geom_text(data = events, mapping = aes(label = text, y = 0), angle = 60, hjust = 0)