如何在ggplot2中为X轴两端添加双标签？

问题背景 #

现有数据框scenario_data结构如下：

name        x    y
Scenario 1  0.5  0.5
Scenario 2  0.2  0.2
Scenario 3  0.8  0.2
Scenario 4  0.2  0.8

当前绘图代码生成的图表中，X轴只有中间的"Middle"标签，需要替换为左侧显示"Low"、右侧显示"High"的两端标签。

原绘图代码 #

library(tidyverse)
library(ggrepel)

scenario_data <- read.csv("scatter_plot.csv", header = T)

tiff("scenario_plot.tiff", units="in", width=5, height=5, res=300)

scenarios_plot <- ggplot(scenario_data,
                         aes(x = x, y = y)) +
  geom_point(colour = "#93358D", size = 3) +
  labs(title = "Figure 1: Four \n Scenarios",
       x = "Middle",
       y = "Scale of \n Intervention")

scenarios_plot +
  geom_label_repel(aes(label = name),
                   box.padding = 0.35,
                   point.padding = 0.5,
                   segment.color = "grey50") +
  theme_classic() +
  theme(axis.text.x=element_blank(),
        axis.title.y=element_text(angle = 0),
        axis.ticks.x=element_blank(),
        axis.text.y=element_blank(),
        axis.ticks.y=element_blank(),
        plot.title = element_text(hjust=0.5),
        axis.line = element_line(arrow = 
                                   arrow(angle = 15, length = 
                                           unit(0.15, "inches"), 
                                         type = "closed")))
dev.off()

（注：原代码存在labs()未闭合的语法错误，已补充修正）

解决方案 #

通过annotate()直接在X轴两端添加文本标签，同时移除原X轴标题，具体步骤如下：

1. 移除原X轴标题，将labs()中的x = "Middle"改为x = NULL
2. 使用annotate()分别在X轴左端（x=0位置）和右端（x=1位置）添加"Low"和"High"标签，调整y值让标签对齐到轴下方
3. 增加底部绘图边距，避免标签被截断

修正后的完整代码 #

library(tidyverse)
library(ggrepel)

scenario_data <- read.csv("scatter_plot.csv", header = T)

tiff("scenario_plot.tiff", units="in", width=5, height=5, res=300)

scenarios_plot <- ggplot(scenario_data,
                         aes(x = x, y = y)) +
  geom_point(colour = "#93358D", size = 3) +
  labs(title = "Figure 1: Four \n Scenarios",
       x = NULL,  # 移除原X轴标题
       y = "Scale of \n Intervention") +
  geom_label_repel(aes(label = name),
                   box.padding = 0.35,
                   point.padding = 0.5,
                   segment.color = "grey50") +
  # 添加两端标签
  annotate("text", x = 0, y = -0.05, label = "Low", size = 4) +
  annotate("text", x = 1, y = -0.05, label = "High", size = 4) +
  theme_classic() +
  theme(axis.text.x=element_blank(),
        axis.title.y=element_text(angle = 0),
        axis.ticks.x=element_blank(),
        axis.text.y=element_blank(),
        axis.ticks.y=element_blank(),
        plot.title = element_text(hjust=0.5),
        axis.line = element_line(arrow = 
                                   arrow(angle = 15, length = 
                                           unit(0.15, "inches"), 
                                         type = "closed")),
        plot.margin = margin(b = 20, unit = "pt"))  # 增加底部边距防止标签截断

print(scenarios_plot)
dev.off()

说明 #

• annotate()的x参数设置为0（左端点）和1（右端点），匹配X轴数据的取值范围（0-1）
• y = -0.05用于将标签定位在X轴下方，可根据实际绘图比例微调该值
• plot.margin增加底部边距，确保标签不会被输出的图片截断

内容的提问来源于stack exchange，提问作者HelpMe