如何为ggplot图表添加分组空白与额外X轴标签

需要制作以var为X轴的geom_point图表，var分为以下三大组：

• Strength组：Weak、Strong
• Race/Ethnicity组：White、Black、Hispanic
• City组：Springfield、Buxton、Artowne、Friedsville、Alexandria、Oldmill

同时要求：

1. 各组之间添加空白间隔
2. 除Total外，每个大组下方添加居中的组标签（如Race/Ethnicity组下方添加对应组名标签）

原始代码与示例数据如下：

order1 <- c("Total", "Weak", "Strong", "White", "Black", "Hispanic", "Springfield", "Buxton", "Artowne", "Friedsville", "Alexandria", "Oldmill")

data %>% 
  ggplot(., aes(y = mean, x = var, color = var)) +
  geom_point() +
  geom_pointrange(aes(ymin = lower, ymax = upper)) +
  scale_x_discrete(limits = order1) +
  labs(x = NULL) +
  theme_classic() +
  theme(legend.position = "none")

示例数据：

structure(list(category = c("points", "points", "points", "points", 
"points", "points", "points", "points", "points", "points", "points", 
"points"), var = c("Total", "Weak", "Strong", "White", "Black", 
"Hispanic", "Springfield", "Buxton", "Artowne", "Friedsville", 
"Alexandria", "Oldmill"), mean = c(175, 145, 160, 120, 200, 200, 
225, 200, 100, 160, 120, 100), lower = c(156, 120, 140, 100, 
168, 141, 191, 72, 45, 130, 100, 40), upper = c(190, 176, 185, 
150, 245, 240, 280, 340, 230, 200, 150, 150)), class = c("tbl_df", 
"tbl", "data.frame"), row.names = c(NA, -12L))

可以通过插入空X轴水平实现组间空白，结合annotate添加组标签来实现需求，具体步骤如下：

1. 调整X轴顺序，插入空水平
   在原始的order1中插入空字符串作为组间隔，让X轴自动留出空白：

# 插入空水平作为组间间隔
order1 <- c("Total", "", 
            "Weak", "Strong", "", 
            "White", "Black", "Hispanic", "", 
            "Springfield", "Buxton", "Artowne", "Friedsville", "Alexandria", "Oldmill")

2. 添加组标签并调整图表
   使用annotate()在各组中心位置添加自定义标签，同时调整主题避免标签重叠：

library(ggplot2)

# 加载数据
data <- structure(list(category = c("points", "points", "points", "points", 
"points", "points", "points", "points", "points", "points", "points", 
"points"), var = c("Total", "Weak", "Strong", "White", "Black", 
"Hispanic", "Springfield", "Buxton", "Artowne", "Friedsville", 
"Alexandria", "Oldmill"), mean = c(175, 145, 160, 120, 200, 200, 
225, 200, 100, 160, 120, 100), lower = c(156, 120, 140, 100, 
168, 141, 191, 72, 45, 130, 100, 40), upper = c(190, 176, 185, 
150, 245, 240, 280, 340, 230, 200, 150, 150)), class = c("tbl_df", 
"tbl", "data.frame"), row.names = c(NA, -12L))

# 定义X轴顺序（含空水平）
order1 <- c("Total", "", 
            "Weak", "Strong", "", 
            "White", "Black", "Hispanic", "", 
            "Springfield", "Buxton", "Artowne", "Friedsville", "Alexandria", "Oldmill")

# 绘制图表
data %>% 
  ggplot(aes(y = mean, x = var, color = var)) +
  geom_point(size = 3) +
  geom_pointrange(aes(ymin = lower, ymax = upper)) +
  scale_x_discrete(limits = order1) +
  # 添加组标签，定位到各组中心位置
  annotate("text", x = 3, y = min(data$lower) - 15, label = "Strength", size = 4, fontface = "bold") +
  annotate("text", x = 6.5, y = min(data$lower) - 15, label = "Race/Ethnicity", size = 4, fontface = "bold") +
  annotate("text", x = 12, y = min(data$lower) - 15, label = "City", size = 4, fontface = "bold") +
  labs(x = NULL, y = "Mean Value") +
  theme_classic() +
  theme(
    legend.position = "none",
    # 调整X轴标签上下间距，避免和组标签重叠
    axis.text.x = element_text(margin = margin(t = 10))
  )

3. 代码说明

• 插入空水平：在order1中加入空字符串，让X轴在组之间自动产生空白间隔
• 组标签定位：通过x参数指定标签的X轴位置（对应调整后的order1索引，从1开始），y参数设置在所有数据点下方，避免遮挡
• 主题调整：通过axis.text.x的margin参数调整X轴标签的上下间距，防止和组标签重叠

内容的提问来源于stack exchange，提问作者a_todd12