Distinguish theme (background) color for negative and positive values in geom

For data of this type:

set.seed(123)
df <- data.frame(
  Q = c(rep("q_pol",10), rep("q_wh",10)),
  slope = c(rnorm(10,-0.5), rnorm(10, 0.5)),
  Recipient = rep(c("A", "B"),10)
)

how can I color the theme (or background) of these boxplots in two different colors: the upper half for values > 0, say, "lightblue" and the lower half for values < 0, say, "darkblue":

library(ggplot2)
ggplot(df, 
       aes(x = Q, y = slope, color = Recipient))   
  geom_boxplot(notch = TRUE)

CodePudding user response：

One option would be to add different filled backgrounds using geom_rect:

library(ggplot2)

ggplot(df, 
       aes(x = Q, y = slope, color = Recipient))   
  geom_rect(data = data.frame(
    xmin = c(-Inf, -Inf),
    xmax = c(Inf, Inf),
    ymin = c(-Inf, 0),
    ymax = c(0, Inf),
    fill = c("darkblue", "lightblue")
  ), aes(xmin = xmin, xmax = xmax, ymin = ymin, ymax = ymax, fill = fill), inherit.aes = FALSE, alpha = .5)  
  scale_fill_manual(values = c("darkblue" = "darkblue", "lightblue" = "lightblue"), guide = "none")  
  geom_boxplot(notch = TRUE)