colorful histogram

library(data.table)
library(ggplot2)

# data generation
colors <- rainbow(20)
DT <- data.table(x = runif(1e4), grp = sample(LETTERS[1:10], 1e4, TRUE))
breaks <- seq(0, 1, by = 0.05)
DT[ , color := colors[findInterval(x, breaks)]]
ggplot(DT, aes(x)) +
  stat_bin(aes(fill = color), breaks = breaks, show.legend = FALSE) +
  facet_wrap(~grp, 5, 2)

# percentage
ggplot(DT, aes(x)) +
  stat_bin(aes(fill = color, y = (..count..)/sum(..count..)),
           breaks = breaks, show.legend = FALSE) +
  facet_wrap(~grp, 5, 2) + labs(y = "Percentage")