ggplot: Cover `facet_grid` title with rectangle

问题

This is an extension/hack to a similar question that I asked here.

I Created a graph in ggplot and I want to cover the titles of a facet_grid with a rectangle.

Using geom_rect I manged to spread rectangles over each facet. However, how can I spread the rectangles over the titles?

Current graph:

Expected graph:

Sample data and script:

library(tidyverse)

df <- head(mtcars, 5)

plot <- df %>% 
  ggplot(aes(gear, disp)) + 
  geom_bar(stat = "identity") + 
  facet_grid(~am + carb,
             space = "free_x", 
             scales = "free_x") +
  ggplot2::theme(
    panel.spacing.x = unit(0,"cm"), 
    axis.ticks.length=unit(.25, "cm"), 
    strip.placement = "outside",
    legend.position = "top",
    legend.justification = "center",
    legend.direction = "horizontal",
    legend.key.size = ggplot2::unit(1.5, "lines"),
    # switch off the rectangle around symbols
    legend.key = ggplot2::element_blank(),
    legend.key.width = grid::unit(2, "lines"),
    # # facet titles
    strip.background = ggplot2::element_rect(
      colour = "black",
      fill = "white"),
    panel.background = ggplot2::element_rect(
      colour = "white",
      fill = "white"), 
    panel.grid.major = element_blank(),
    panel.grid.minor = element_blank())

plot + 
  geom_rect(aes(xmin=2.4, xmax=2.7, ymin=400, ymax=300),
            color="black", fill="white") +
  geom_text(aes(x = 2.5, y = 400, label="world"), size=2)

回答1:

As pointed out in the related post, one can now easily created nested facets with the ggnomics package, available on GitHub.

This does not quite exactly what you were asking here (annotating outside the plot area with rectangles that go across facets) but probably achieves what you want in the end... Annotating across facets would require another grob hack...

#devtools::install_github("teunbrand/ggnomics")
  library(ggnomics)
#> Loading required package: ggplot2
  library(tidyverse)

  mydat<- head(mtcars, 5)
  mydat %>% 
    ggplot(aes(gear, disp)) + 
    geom_bar(stat = "identity") + 
    facet_nested(~am + carb) +
    theme(panel.spacing.x = unit(0,"cm"), 
          axis.ticks.length=unit(.25, "cm"), 
          strip.placement = "inside",
          strip.background = element_rect( colour = "black", fill = "white"),
          panel.background = element_rect( colour = "black", fill = "white"))

^{Created on 2020-03-24 by the reprex package (v0.3.0)}

来源：https://stackoverflow.com/questions/60827811/ggplot-cover-facet-grid-title-with-rectangle

标签

ggplot2

facet-grid