如何更改ggplot对象条带区域某些边框的颜色？

Question

剧情代码：

library(tidyverse)

mtcars %>% 
  ggplot(aes(factor(cyl), disp)) +
  geom_col() +
  facet_grid(. ~ gear, switch = "x") +
  theme(
    strip.placement = "outside",
    strip.background = element_rect(fill = "white", color = "red")
  )

我正在尝试修改某些边框的颜色：预期输出：

我尝试使用 grobs 更改它，但似乎无法更改特定边框。

p <- mtcars %>% 
  ggplot(aes(factor(cyl), disp)) +
  geom_col() +
  facet_grid(. ~ gear, switch = "x") +
  theme(
    strip.placement = "outside",
    strip.background = element_rect(fill = "white", color = "red")
  )

g <- ggplotGrob(p)
g$grobs[[13]]$grobs[[1]]$children$strip.background.x..rect.33641$gp$col

Answer 1

根据的回答，您可以使用 linesGrob 更改边框。在您的情况下，您将需要 polylineGrob 因为您需要两条未连接的线（在网格的每一侧各一条）。

代码

p <- mtcars %>% 
  ggplot(aes(factor(cyl), disp)) +
  geom_col() +
  facet_grid(. ~ gear, switch = "x") +
  theme(
    strip.placement = "outside",
    strip.background = element_rect(color = NA)
  )

library(grid)
q <- ggplotGrob(p)

lr2 <-  polylineGrob(x=c(0,0,1,1),
                      y=c(0,1,0,1),
                      id=c(1,1,2,2),
                      gp=gpar(col="blue", lwd=3))

for (k in grep("strip-b",q$layout$name)) {
  q$grobs[[k]]$grobs[[1]]$children[[1]] <- lr2
}

grid.draw(q)

情节

如何更改ggplot对象条带区域某些边框的颜色？

How to change color of certain border of strip area of ggplot object?

grid

r

ggplot2