R: Overlay density plots by condition and by average plot

Question

I am able to create both density plots shown using the code provided. What I am hoping to do is create one graph combining the two. Essentially I want to overlay the black line on top of the plot colored by condition.

d1 <- ggplot(df, aes(x=a)) + geom_density()

d2 <- ggdensity(biolReps, x = "a", color = "b",fill = "b"

It's easier to help you if you include a simple [reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) with sample input that can be used to test and verify possible solutions. — MrFlick, Nov 04 '21 at 03:18

Jon Spring · Accepted Answer · 2021-11-06T03:21:14.087

Is this what you're going for? I use after_stat here to scale down the conditional density plots to be comfortably lower than the total density. (which, being by definition less spiky, will tend to have lower peak densities than the conditional densities.)

ggplot(mtcars) +
  geom_density(aes(mpg)) +
  geom_density(aes(mpg, after_stat(count) * 0.01, 
                   group = cyl, fill = as.character(cyl)), alpha = 0.2)

If you want to convert this to a function, you could use something like the following. The {{ }} or "embrace" operator works to forward the variable names into the environment of the function. More at https://rlang.r-lib.org/reference/topic-data-mask-programming.html#embrace-with-

plot_densities <- function(df, var, group) {
  ggplot(df) +
    geom_density(aes( {{ var }} )) +
    geom_density(aes( {{ var }}, after_stat(count) * 0.01, 
                     group = {{ group }}, 
                     fill = as.character( {{ group }} )), alpha = 0.2)
}

plot_densities(mtcars, mpg, cyl)

I am hoping to turn this into a function so I can reuse on multiple columns. I can get the total density plot this way using `ggplot(df) + geom_density(aes_string(column))` where column is passed to the function as "columnName" but I cannot get the aes_string to work with the second part of the code. Is this an easy fix? — keenan, Nov 05 '21 at 23:49

R: Overlay density plots by condition and by average plot

1 Answers1