如何在ggplot2中将stat_summary绘制于图表外部上方？

要把stat_summary的统计文本移到图表外部，最简便的方式是提前计算分组统计数据，再通过geom_text将文本定位到扩展后的坐标轴区域，同时调整边距避免文本截断。以下是修改后的完整代码：

步骤1：定义统计函数并预处理统计数据 #

library(dplyr)
library(ggplot2)

# 定义统计文本生成函数（修正原代码中std()为R内置的sd()）
stats_PFAS10 <- function(y) {
  paste(
    "Anzahl =", length(y), "\n",
    "Mittelwert =", round(mean(y), 2), "\n",
    "KI1 = ", round(mean(y) - qnorm(0.95)*sd(y)/sqrt(length(y)), 2), "\n",
    "KI2 = ", round(mean(y) + qnorm(0.95)*sd(y)/sqrt(length(y)), 2), "\n",
    "1.Q = ", quantile(y, probs=0.25, na.rm=TRUE), "\n",
    "Median =", round(median(y), 2), "\n",
    "3.Q = ", quantile(y, probs=0.75, na.rm=TRUE), "\n",
    "90 % Q = ", quantile(y, probs=0.9, na.rm=TRUE), "\n",
    "STD = ", round(sd(y),2), "\n", 
    "Varianz =", round(var(y),2), "\n",
    "Max =", round(max(y),2), "\n",
    "Min =", round(min(y),2)
  )
}

# 按Quelle和Probenart分组计算统计文本
stats_data <- PFAS_data %>%
  mutate(Quelle = factor(Quelle, levels=c('Siedlung', 'Hauptpunktquelle')),
         Probenart = factor(Probenart, levels=c('OBER-0-20', 'UNTER20-40'))) %>%
  group_by(Quelle, Probenart) %>%
  summarise(label = stats_PFAS10(pfas10), .groups = "drop")

# 计算x轴（翻转后为y轴）的扩展范围，预留文本空间
max_pfas <- max(PFAS_data$pfas10, na.rm = TRUE)
x_extend <- max_pfas * 1.3  # 扩展30%空间，可根据文本长度调整

步骤2：绘制图表并添加外部统计文本 #

PFAS_data %>%
  mutate(Quelle = factor(Quelle, levels=c('Siedlung', 'Hauptpunktquelle')),
         Probenart = factor(Probenart, levels=c('OBER-0-20', 'UNTER20-40'))) %>%
  ggplot(mapping = aes(x = pfas10, y = Probenart))+
  geom_boxplot(aes(fill = Probenart), col = "black", outlier.size = 2, outlier.shape = 1, width=0.5, na.rm = TRUE)+
  geom_jitter(width  = 0.1, color = "grey46", na.rm = TRUE )+
  facet_grid(~ Quelle, scale = "free", space = "free") +
  stat_boxplot(geom = 'errorbar', width = 0.2, na.rm = TRUE) +  
  # 将统计文本放置到扩展后的右侧区域
  geom_text(data = stats_data, aes(x = x_extend, y = Probenart, label = label), 
            hjust = 0, vjust = 0.5, size = 3) +
  # 设定x轴范围，预留文本空间
  coord_flip(xlim = c(0, x_extend)) +
  theme_bw() +
  theme(legend.position="bottom",
        axis.title.x = element_text(size=11),
        axis.text.x = element_blank(), 
        axis.title.y = element_text(size=14), 
        axis.text.y = element_text(size=12),
        strip.text.x = element_text(size = 12, face = "bold"),
        legend.background = element_rect(size=0.5, linetype="solid", colour ="black"),
        text=element_text(family="sans"),
        # 增加右侧边距，避免文本被截断
        plot.margin = margin(5, 60, 5, 5))

关键调整说明 #

• 提前计算统计数据：避免stat_summary在图表内部占用空间，同时更精准控制文本位置。
• 扩展坐标轴范围：通过x_extend设置超出数据最大值的范围，为文本预留空间。
• 调整边距：plot.margin增加右侧边距，确保统计文本完整显示。
• 文本对齐：hjust=0让文本左对齐，紧贴图表数据区域，视觉上更协调。

内容的提问来源于stack exchange，提问作者Celina Steffani