ggplot2 shade area under density curve by group

Question

I have this dataframe:

set.seed(1)
x <- c(rnorm(50, mean = 1), rnorm(50, mean = 3))
y <- c(rep(\"site1\", 50), rep(\"site2\", 50))
xy <- data.frame(         


        

Answer 1

The problem with @jlhoward's solution is that you need to manually add goem_ribbon for each group you have. I wrote my own ggplot stat wrapper following this vignette. The benefit of this is that it automatically works with group_by and facet and you don't need to manually add geoms for each group.

StatAreaUnderDensity <- ggproto(
  "StatAreaUnderDensity", Stat,
  required_aes = "x",
  compute_group = function(data, scales, xlim = NULL, n = 50) {
    fun <- approxfun(density(data$x))
    StatFunction$compute_group(data, scales, fun = fun, xlim = xlim, n = n)
  }
)

stat_aud <- function(mapping = NULL, data = NULL, geom = "area",
                    position = "identity", na.rm = FALSE, show.legend = NA, 
                    inherit.aes = TRUE, n = 50, xlim=NULL,  
                    ...) {
  layer(
    stat = StatAreaUnderDensity, data = data, mapping = mapping, geom = geom, 
    position = position, show.legend = show.legend, inherit.aes = inherit.aes,
    params = list(xlim = xlim, n = n, ...))
}

Now you can use stat_aud function just like other ggplot geoms.

set.seed(1)
x <- c(rnorm(500, mean = 1), rnorm(500, mean = 3))
y <- c(rep("group 1", 500), rep("group 2", 500))
t_critical = 1.5

tibble(x=x, y=y)%>%ggplot(aes(x=x,color=y))+
  geom_density()+
  geom_vline(xintercept = t_critical)+
  stat_aud(geom="area",
           aes(fill=y),
           xlim = c(0, t_critical), 
              alpha = .2)

tibble(x=x, y=y)%>%ggplot(aes(x=x))+
  geom_density()+
  geom_vline(xintercept = t_critical)+
  stat_aud(geom="area",
           fill = "orange",
           xlim = c(0, t_critical), 
              alpha = .2)+
  facet_grid(~y)