OP要求的更新：

代码：

library(ggpubr)

# create fake data mtcars1
mtcars1 <- mtcars %>% 
  add_row(mtcars[1,]) %>% 
  mutate(group = rep(c("A", "B", "C"), 11))

compare_means(disp ~ cyl, data = mtcars1,  method = "t.test")
my_comparisons <- list( c("4", "6"), c("6", "8"), c("4", "8") )

ggboxplot(mtcars1, x = "cyl", y = "disp", fill = "cyl", add = "jitter") +
  scale_fill_manual(values=c("#0433ff", "#fe403f", "#66cd00")) +
  stat_compare_means(comparisons = my_comparisons)+
  stat_compare_means(label.y = 700) +
  facet_grid(.~group, switch = "x")+
  xlab(NULL) +
  theme(strip.background = element_blank(),
        strip.placement = "outside")

下面是使用ggpubr包和mtcars数据集的示例：

library(ggpubr)

compare_means(disp ~ cyl, data = mtcars,  method = "t.test")
my_comparisons <- list( c("4", "6"), c("6", "8"), c("4", "8") )

ggboxplot(mtcars, x = "cyl", y = "disp", color = "cyl", add = "jitter") +
  stat_compare_means(comparisons = my_comparisons)+
  stat_compare_means(label.y = 700)