如何将单个注释添加到具有多个y轴的图形

Question

我希望添加垂直线条和标签，以引起对ggplot2图形x轴上特定日期的注意。线条和标签将注意力集中在同一日期的多个变量上，这些变量构建在彼此之上。我的问题是，我只想展示每个标签一次，但我的尝试是将标签贴在每个标签上。 y轴图。

我已经模拟了一些虚拟数据来说明。为避免疑问，我希望实现的是在第一条垂直线上带有文字＆＃34; A＆＃34;的单个标签，以及＆＃34; B＆＃34;和＆＃34; C＆＃34;在第二行和第三行，目前我每行都有三个标签。

library(ggplot2)
library(reshape2)
library(dplyr)
library(scales)

set.seed(1234)
PetSightings = data.frame(DateRange = seq(as.Date("2016/1/1"), by = "day", length.out = 60),
                      cats = round(rnorm(60, 10, 3), 0), dogs = round(rnorm(60, 20, 10), 0),
                      parrots = round(rnorm(30, 5, 2)))

PetSightingsMelt = melt(PetSightings, id.vars = "DateRange")


ggplot(PetSightingsMelt, aes(x = DateRange, y = value)) +  
  ggtitle("Pet Sightings") +
  labs(x = "Date", y = "Values") +
  geom_bar(stat = "identity", aes(colour = variable)) +
  geom_vline(xintercept = as.numeric(PetSightings$DateRange[15]), linetype = "longdash", alpha = 0.5) +
  geom_vline(xintercept = as.numeric(PetSightings$DateRange[45]), linetype = "longdash", alpha = 0.5) +
  geom_vline(xintercept = as.numeric(PetSightings$DateRange[55]), linetype = "longdash", alpha = 0.5) +
  annotate("text", x = PetSightings$DateRange[15], y = 25, label = "A", size = 6) +
  annotate("text", x = PetSightings$DateRange[45], y = 25, label = "B", size = 6) +
  annotate("text", x = PetSightings$DateRange[55], y = 25, label = "C", size = 6) +
  facet_grid(variable ~ ., scales = "free_y") +
  theme(legend.position = "none",
    axis.text.x = element_text(angle = 60, vjust = 0.5, size = 6),
    plot.title = element_text(size = 20),
    axis.text.x = element_text(size = 10),
    axis.title.x = element_text(face = "bold", size = 12),
    axis.title.y = element_text(face = "bold", size = 12),
    axis.text.y = element_text(size = 8),
    strip.text.y = element_text(size = 10, angle = 0)) + 
  scale_x_date(labels = date_format("%Y-%m"), date_breaks = "1 month") +
  scale_y_continuous(labels = comma)

Answer 1

似乎我们无法使用annotate来做到这一点。因此，我们可以创建一个数据框，用于将特定的geom_text放到图上。我们假设我们创建数据框ann_label，如下所示：

ann_label <- data.frame(DateRange = PetSightings$DateRange[c(15, 45, 55)], value = 25, label = LETTERS[1:3],
                        variable = factor("cats", level = c("cats", "dogs", "parrots")))

然后，您只需将geom_text添加到ggplot对象：

+ geom_text(data = ann_label, aes(label = label), size = 6)

结果：