R ggplot background color boxplot

Question

I have a dataframe like this one:

value = runif(n = 1000) 
type = rep(c("a","b","c","d"),250) 
type2 = rep(c("a","b"),500) 
number = sample(1:4, 1000, replace=TRUE, prob=c(0.25, 0.25, 0.25, 0.25) )
feature = c(rep("small",500),rep("big",500)) 
allResults <- data.frame(value,type,type2,number,feature)

I'd like to color the background of boxplot by type2 value. If i use fill and col, it's not very clear. I think is more intutitive the background color if is possible.

library("ggplot2")
ggplot(allResults, aes(y=value, x=type)) + geom_boxplot(alpha=.3, aes(fill = type,col=type2)) +
  ggtitle("comparison") + facet_grid(feature ~ number) +
  theme(legend.position = "bottom",axis.text.x = element_text(angle = 90, hjust = 1)) +
  scale_y_continuous(breaks =  seq(0, 1, by = 0.05),limits = c(0,1))

This is my result at the moment:

I have seen that is possible to color the backgroud using geom_rect() but I don't understand how to apply.

Answer 1

You could use geom_rect and set your divisions. I originally had a and b as your rects factors, but to match colors in your type fill just set them to a and c.

value = runif(n = 1000) 
type = rep(c("a","b","c","d"),250) 
type2 = rep(c("a","b"),500) 
number = sample(1:4, 1000, replace=TRUE, prob=c(0.25, 0.25, 0.25, 0.25) )
feature = c(rep("small",500),rep("big",500))
nFac <- 4 # define number of factors (types) here
rects <- data.frame(xmin = head(seq <- seq(0.5, nFac + .5, 1), -1), 
                  xmax = tail(seq, -1), rect_type = c("a", "c")) #set your divisions here

allResults <- data.frame(value,type,type2,number,feature, rects)

ggplot(allResults, aes(y=value, x=type)) + geom_boxplot(aes(fill = type, col=type2)) +
  geom_rect(aes(xmin = xmin, xmax = xmax, ymin = -Inf, ymax = Inf, fill = rect_type), alpha = 0.009) +
  ggtitle("comparison") + facet_grid(feature ~ number) +
  theme(legend.position = "bottom",axis.text.x = element_text(angle = 90, hjust = 1)) +
  scale_y_continuous(breaks =  seq(0, 1, by = 0.05),limits = c(0,1))