Is it somehow possible to create a bar chart in ggplot2 using a multi grouping system as shown in this graph?

Question

[graph][1]

I want to create a bar chart grouping the variables as shown at the bottom of the graph (environmental surfaces and processing steps), is there any geom that allows to create this in ggplot2? [1]: https://i.stack.imgur.com/2rQd9.png

Answer 1

You can get the basics with geom_tile(), but you'll manually have to specify where on the y-axis the tiles need to be placed.

library(ggplot2)

df <- expand.grid(first_level = LETTERS[1:4], second_level = LETTERS[5:7],
                  third_level = LETTERS[8:9])
df$value <- rpois(nrow(df), lambda = 2)

ggplot(df, aes(interaction(second_level, first_level), value)) +
  geom_col(aes(fill = third_level), position = position_dodge()) +
  geom_tile(
    aes(y = -0.1, height = 0.2, fill = second_level),
    colour = "white"
  ) +
  geom_tile(
    aes(y = -0.3, height = 0.2, fill = first_level),
    colour = "white"
  )

To get more control over how every level is displayed, you can use the {ggnewscale} package.

ggplot(df, aes(interaction(second_level, first_level), value)) +
  geom_col(aes(fill = third_level), position = position_dodge()) +
  scale_fill_manual(values = c("blue", "yellow")) +
  ggnewscale::new_scale_fill() +
  geom_tile(
    aes(y = -0.1, height = 0.2, fill = second_level),
    colour = "white"
  ) +
  scale_fill_manual(values = c("red", "blue", "grey")) +
  ggnewscale::new_scale_fill() +
  geom_tile(
    aes(y = -0.3, height = 0.2, fill = first_level),
    colour = "white"
  ) +
  scale_fill_manual(values = c("purple", "cyan", "yellow", "green")) +
  scale_y_continuous(expand = c(0, 0, 0.05, 0)) 

^{Created on 2022-05-17 by the reprex package (v2.0.1)}