如何将Patchwork组合图标题置于边框外并绘制圆角边框？

把标题移到边框外部 #

要让标题在边框外面，得把边框只套在拼接好的三张图上，标题单独放在边框上方。用wrap_elements()给拼接后的绘图加边框，再单独添加标题即可：

library(ggplot2)
library(patchwork)

# 先定义带圆角的边框主题（顺便解决第二个问题）
theme_rounded_border <- theme_gray() + 
  theme(plot.background = element_rect(fill = NA, colour = 'black',
                                       size = 1, linetype = "dashed",
                                       radius = unit(5, "mm"))) # 设置圆角半径

# 先拼接三张图
plot_combined <- ggplot() + ggplot() + ggplot() + 
  plot_layout(ncol=1, guides = "collect")

# 给拼接好的图套边框，再加上标题
wrap_elements(plot_combined) + theme_rounded_border +
  plot_annotation(title = "Pred Sp") &
  theme(plot.title = element_text(margin = margin(b = 10))) # 给标题加底部间距，避免和边框挤在一起

绘制带圆角的边框 #

直接在element_rect()里添加radius参数就能实现圆角，单位用unit()指定（比如毫米、点）。如果不需要调整标题位置，仅修改原有主题即可：

theme_rounded_border <- theme_gray() + 
  theme(plot.background = element_rect(fill = NA, colour = 'black',
                                       size = 1, linetype = "dashed",
                                       radius = unit(5, "mm")))

ggplot() + ggplot() + ggplot() + 
  plot_layout(ncol=1, guides = "collect") + 
  plot_annotation(title = "Pred Sp", theme = theme_rounded_border)

内容的提问来源于stack exchange，提问作者Tianjian Qin