Adding shading alternate areas for categorical variable in a bar plot in ggplot2

Question

I am trying t o plot a bar plot using ggplot2as follows:

library(ggplot2)
ggplot(mtcars, aes(factor(carb))) +
  geom_bar() +
  coord_flip()
<         


        

Answer 1

Perhaps something along these lines where you overlay the wider shaded bars, which vary in color, with the darker smaller bar?

ggplot(mtcars, aes(factor(carb))) +
  geom_bar(width = 1.1, aes(x = factor(carb), fill = ifelse(mtcars$carb %in% c(1,3,6), "blue", "transparent"))) +
  guides(fill = FALSE) +
  geom_bar(width = 0.7) +
  scale_fill_manual(values = c("transparent", "blue")) +
  coord_flip()

Answer 2

Solved it

# Create data.frame with shading info
shading <- data.frame(min = seq(from = 0.5, to = max(as.numeric(as.factor(mtcars$carb))), by = 1),
           max = seq(from = 1.5, to = max(as.numeric(as.factor(mtcars$carb))) + 0.5, by = 1),
           col = c(0,1))

# Plot
ggplot() +
  geom_bar(data = mtcars, mapping = aes(factor(carb))) +
  geom_rect(data = shading,
            aes(xmin = min, xmax = max, ymin = -Inf, ymax = Inf,
                fill = factor(col), alpha = 0.1)) +
  scale_fill_manual(values = c("white", "gray53")) +
  geom_bar(data = mtcars, mapping = aes(factor(carb))) +
  coord_flip() +
  guides(fill = FALSE, alpha = FALSE)