如何在ggplot2分面绘图顶部为分组列添加A、B标签及空白分隔列

你可以通过两种方案实现需求，都可以避免拼接时绘图区不对齐的问题：

方案1：使用ggh4x包嵌套分面（推荐） #

该方案直接在单张ggplot内实现分层标题和空白分隔，不需要拼接。

步骤1：数据预处理 #

先给你的数据添加上层分组标签，同时插入一个虚拟空白项作为两组分面的分隔：

library(tidyverse)
library(ggh4x)

# 整理绘图数据
plot_data <- data.QC.1[!data.QC.1$hemiparasite %in% c("TRER", "TRVE", "CAHI"),] %>%
  mutate(
    # 定义hemiparasite的顺序：前4个A组 → 空白分隔 → 后4个B组，可根据你的实际水平数量调整索引
    hemiparasite = factor(hemiparasite, levels = c(
      levels(hemiparasite)[1:4],
      "blank",
      levels(hemiparasite)[5:8]
    )),
    # 上层分组标签
    top_group = case_when(
      hemiparasite %in% levels(hemiparasite)[1:4] ~ "A",
      hemiparasite %in% levels(hemiparasite)[6:9] ~ "B",
      TRUE ~ ""
    )
  )

步骤2：修改ggplot代码 #

替换原有的facet_grid为facet_nested，同时设置隐藏空白分面的样式：

Carbon.p <- ggplot(plot_data, aes(x=type.full, y = Value))+
  stat_summary(fun = "mean", shape = "-", size = 2.5)+
  geom_jitter(aes(color = type.full), alpha = 0.5)+ # 注意你原代码这里多了一个右括号，已删除
  scale_color_manual(values = c("#de2d26" ,"#9ebcda", "#8856a7")) +  
  # 嵌套分面设置
  facet_nested(host ~ top_group + hemiparasite, 
               scales= "free", 
               switch = "y",
               nest_line = element_blank(),
               strip = strip_nested(
                 text_x = elem_list_text(
                   element_text(), # 上层A/B标题样式
                   element_text(), # 下层hemiparasite标签样式
                   element_text(color = NA) # 隐藏空白项的标签
                 ),
                 background_x = elem_list_rect(
                   element_rect(),
                   element_rect(),
                   element_rect(fill = NA, color = NA) # 隐藏空白项的标签背景
                 )
               ))+
  theme_bw()+
  theme(text = element_text(size = 10),
        panel.grid.minor = element_blank(),
        panel.grid.major = element_blank(),
        axis.line.x = element_blank(),
        axis.text.y = element_blank(),
        axis.ticks.y = element_blank(),
        axis.line.y = element_blank(),
        legend.title= element_blank(),
        legend.position = "bottom",
        axis.text.x = element_blank(),
        axis.ticks.x = element_blank(),
        legend.key = element_blank(), 
        strip.background = element_rect(colour="black", fill="white"),
        # 隐藏空白分面的背景和边框
        panel.background = element_rect(fill = c(rep("white",4), NA, rep("white",4)), color = NA),
        panel.border = element_rect(color = c(rep("black",4), NA, rep("black",4))))+
  labs(x = NULL,
       y = expression("d13C"),
       title = NULL)

方案2：patchwork拼接对齐法 #

如果你不想额外安装ggh4x包，也可以用patchwork拼接时强制对齐绘图区：

library(patchwork)

# 拆分两组数据
data_A <- filter(plot_data, top_group == "A")
data_B <- filter(plot_data, top_group == "B")

# 绘制A组图，保留y轴
pA <- ggplot(data_A, aes(x=type.full, y = Value))+
  stat_summary(fun = "mean", shape = "-", size = 2.5)+
  geom_jitter(aes(color = type.full), alpha = 0.5)+
  scale_color_manual(values = c("#de2d26" ,"#9ebcda", "#8856a7")) +  
  facet_grid(host ~ hemiparasite, scales= "free", switch = "y")+
  theme_bw()+
  theme(
    # 通用主题和原代码保持一致即可
  )+
  labs(title = "A", y = expression("d13C"))+
  theme(plot.title = element_text(hjust = 0.5))

# 绘制B组图，移除y轴元素
pB <- ggplot(data_B, aes(x=type.full, y = Value))+
  stat_summary(fun = "mean", shape = "-", size = 2.5)+
  geom_jitter(aes(color = type.full), alpha = 0.5)+
  scale_color_manual(values = c("#de2d26" ,"#9ebcda", "#8856a7")) +  
  facet_grid(host ~ hemiparasite, scales= "free", switch = "y")+
  theme_bw()+
  theme(
    # 通用主题和原代码保持一致即可
    axis.text.y = element_blank(),
    axis.ticks.y = element_blank()
  )+
  labs(title = "B", y = NULL)+
  theme(plot.title = element_text(hjust = 0.5))

# 拼接对齐，中间插入空白占位
pA + plot_spacer() + pB + 
  plot_layout(widths = c(4, 0.1, 4), guides = "collect") &
  theme(legend.position = "bottom")

内容的提问来源于stack exchange，提问作者Skotani1