r - R ggplot2：更改刻面条中字体和背景的颜色？

Question

我正在尝试自定义包含构面的 ggplot2 图，并且想更改构面条的颜色以及字体的颜色。我找到了一些代码来改变strip.background颜色，但无法修改它来改变字体颜色......知道吗？

到目前为止我得到了什么：

library(ggplot2)
library(grid)

p <- ggplot(mpg, aes(displ, cty)) + geom_point() + facet_grid(drv ~ cyl) +
  ggtitle("How to change coloour of font in facet strip?")

g <- ggplot_gtable(ggplot_build(p))
strip_both <- which(grepl('strip-', g$layout$name))
fills <- c("red","green","blue","yellow","red","green","blue","yellow")
k <- 1

for (i in strip_both) {
  j <- which(grepl('rect', g$grobs[[i]]$grobs[[1]]$childrenOrder))
  g$grobs[[i]]$grobs[[1]]$children[[j]]$gp$fill <- fills[k]
  k <- k+1
}
grid.draw(g)

^{由reprex 包（v0.2.1）于 2018 年 11 月 23 日创建}

Answer 1

当然有人可以找到更好的解决方案，但到目前为止我只能这样做：

library(ggplot2)
library(grid)
library(RColorBrewer)

p <- ggplot(mpg, aes(x = displ, y = cty)) + 
  geom_point() + 
  facet_grid(drv ~ cyl) +
  ggtitle("How to change coloour of font in facet strip?") + 
  ggthemes::theme_few()

g <- ggplot_gtable(ggplot_build(p))

strips <- which(grepl('strip-', g$layout$name))

pal <- brewer.pal(8, "Paired")


for (i in seq_along(strips)) {
  k <- which(grepl('rect', g$grobs[[strips[i]]]$grobs[[1]]$childrenOrder))
  l <- which(grepl('titleGrob', g$grobs[[strips[i]]]$grobs[[1]]$childrenOrder))
  g$grobs[[strips[i]]]$grobs[[1]]$children[[k]]$gp$fill <- pal[i]
  g$grobs[[strips[i]]]$grobs[[1]]$children[[l]]$children[[1]]$gp$col <- pal[i + 1]
}

plot(g)

Answer 2

另一种选择是使用grid的编辑功能，前提是我们构建了gPath我们想要编辑的每个 grob。

准备 gPath：

library(ggplot2)
library(grid)

p <- ggplot(mpg, aes(displ, cty)) + geom_point() + facet_grid(drv ~ cyl)

# Generate the ggplot2 plot grob
g <- grid.force(ggplotGrob(p))
# Get the names of grobs and their gPaths into a data.frame structure
grobs_df <- do.call(cbind.data.frame, grid.ls(g, print = FALSE))
# Build optimal gPaths that will be later used to identify grobs and edit them
grobs_df$gPath_full <- paste(grobs_df$gPath, grobs_df$name, sep = "::")
grobs_df$gPath_full <- gsub(pattern = "layout::", 
                            replacement = "", 
                            x = grobs_df$gPath_full, 
                            fixed = TRUE)

查看表格grobs_df并熟悉命名和路径。例如，所有条带都包含关键字“条带”。他们的背景由关键字“background”标识，标题文本由“titleGrob”和“text”标识。然后我们可以使用正则表达式来捕获它们：

# Get the gPaths of the strip background grobs
strip_bg_gpath <- grobs_df$gPath_full[grepl(pattern = ".*strip\\.background.*", 
                                            x = grobs_df$gPath_full)]
strip_bg_gpath[1] # example of a gPath for strip background 
## [1] "strip-t-1.7-5-7-5::strip.1-1-1-1::strip.background.x..rect.5374"

# Get the gPaths of the strip titles
strip_txt_gpath <- grobs_df$gPath_full[grepl(pattern = "strip.*titleGrob.*text.*", 
                                             x = grobs_df$gPath_full)]
strip_txt_gpath[1] # example of a gPath for strip title
## [1] "strip-t-1.7-5-7-5::strip.1-1-1-1::GRID.titleGrob.5368::GRID.text.5364"

现在我们可以编辑 grobs：

# Generate some color
n_cols <- length(strip_bg_gpath)
fills <- rainbow(n_cols)
txt_colors <- gray(0:n_cols/n_cols)

# Edit the grobs
for (i in 1:length(strip_bg_gpath)){
  g <- editGrob(grob = g, gPath = strip_bg_gpath[i], gp = gpar(fill = fills[i]))
  g <- editGrob(grob = g, gPath = strip_txt_gpath[i], gp = gpar(col = txt_colors[i]))
}

# Draw the edited plot
grid.newpage(); grid.draw(g)
# Save the edited plot
ggsave("edit_strips_bg_txt.png", g)