[Feature request] : fill the boundaries within

[jorvlan]

Is there a way to assign different colors to the boundaries within each violin?
We have Likert data, and for each 'item' we would like to have a different color representation inside the violin (i.e., the boundaries you see in the figures below i.e., 2nd figure, which are different from the default 'quantiles' boundaries i.e., 1st figure).
.

Any suggestions would be appreciated!

Please see the code (steps are included on how to create the figure below)!

---

library(ggplot2)
library(reshape2)
library(ggridges)

STEP 1:
Create fake data for visualization of likert data

pre <- c(1,1,4,1,1,2,1,1,2,2,1,3,2,1,2,2,2,3,2,4,5,2,3,3,4,4,2,2,5,3,4,3,5,3,3,4,3,2,2,2,4,2,3,2,3,4,4,3,5,1,2,5,2,3,3,5,5,3,1,3,4,2,3,4,3,3,2,3,4,5,3,3,3,4,2,2,4,3,3,5,3,3,2,2,3,3,1,4,4,2,3,4,2,2,1,2,3,3,3,2,1,2,3,3,3,2,3,4,3,4,3,1,4,2,3,2,4,3,3,4,3,3,2,3,4,3,4,3,3,3)

post <- c(1,1,1,1,1,1,1,2,2,1,1,2,2,3,2,2,2,2,2,2,3,3,2,3,1,4,1,2,3,3,5,2,4,3,4,2,3,2,3,2,3,3,3,3,3,3,4,3,5,3,1,3,2,3,3,2,2,3,3,3,4,3,3,3,3,3,3,4,3,3,3,4,3,4,3,3,2,3,3,3,3,3,1,3,3,2,2,4,5,3,3,4,3,3,2,3,3,4,3,4,1,3,4,2,3,2,4,2,3,3,3,3,4,1,3,4,3,3,3,4,3,3,3,3,3,3,3,4,4,5)

STEP 2:
Do some wrangling & labeling to set up the desired structure

likert_data <- data.frame(pre,post)

likert_data$id <- as.factor(as.character(rep(1:dim(likert_data)[1])))

likert_data <- reshape2::melt(likert_data, id.vars = "id")
colnames(likert_data)[2] <- "time"

likert_data$covariate <- -likert_data$value*2

likert_data$group <- c(rep("old", 65), rep("young", 65), rep("old", 65), rep("young", 65))#,
                # rep("old", 65), rep("young", 200), rep("old", 200), rep("young", 200))

likert_data$value[likert_data$group == "young"] <- likert_data$value[likert_data$group == "young"] + 1

likert_data$value[likert_data$group == "old" & likert_data$time == "t2"] <- likert_data$value[likert_data$group == "old" & 
likert_data$time == "t2"] -2

likert_data$jit <- jitter(likert_data$value, amount = .2)

STEP 3:
Create bounds function that will define the boundaries for likert data in each violin

proportions <- table(likert_data$pre)/length(likert_data$pre)

4*0.107 + 1 + 4*0.261

abs_range <- abs(min(likert_data$pre)) + abs(max(likert_data$pre))

4*0.107 + 1 + 4*0.261 + 4*.37 + 4*.18 + 4*.07 #(you don't need the last boundary)

bounds <- function(x, ...){
  
  l_unique_min1 <- length(unique(x))-1
  vec <- as.numeric(rep(0, l_unique_min1))
  proportions <- as.numeric(table(x)/length(x))

  s <- 0
  for (i in 1:l_unique_min1){
    vec[i] <- proportions[i]*l_unique_min1 + s
    s <- vec[i]
  }

  vec <- vec + min(x)
  
  return(vec)
}

STEP 4:
Change dataframe orientation

ct <- reshape2::melt(likert_data)

STEP 5:
Plot the figure

ggplot(ct, aes(x = value, y = variable, fill = variable)) +
  geom_density_ridges(quantile_lines = T, quantile_fun = bounds, position = position_nudge(y=.2)) +
  geom_boxplot(width = .2, position = position_nudge(y= -.2)) +
  geom_point() +
  scale_x_continuous(limits=c(-15, 20))