How To Add Mean Line to Ridgeline Plot in R with ggridges?

In this article, we will discuss how to add a mean line to the Ridgeline plot in R Programming Language with the ggridges package. 

Ridgeline plot helps us to visualize multiple distributions or a distribution that changes a quantifiable variable. The name “ridgeline” comes from its appearance as an overlapping mountain range. Firstly, we will create a basic ridgeline plot using the diamonds dataset that is a prebuilt data frame in R language natively.

Syntax:

ggplot(dataframe, aes(x , y , fill)) + geom_density_ridges()

Example:

Here is a basic ridgeline plot made using the diamonds dataset. Here, we have used the price and cut variable of the dataset to plot the ridgeline plot. We have used geom_density_ridges() function with the ggplot() function to create the ridgeline plot.

R

# load library ggridges and ggplot2
library(ggridges)
library(ggplot2)

# Diamonds dataset is provided by R natively
# we will use that same dataset for our plot
# basic ridgeline plot
# fill parameter is used to colour them according to their cut type
ggplot(diamonds, aes(x = price, y = cut, fill=cut)) +

# geom_density_ridges() function plots the ridgeline plot
  geom_density_ridges()

Output:

Here, is a basic ridgeline plot plotted using the diamonds dataset. Here, the fill parameter is used to color the plot according to the cut of the diamond.

Adding the mean line

The ridgeline plot with the vertical mean line for each category helps us to understand the variation of the mean over a category of data. To add the mean line to the ridgeline plot with the ggridges, we need to use quantile_lines and quantile_fun parameters inside the geom_density_ridges() function from the ggridges package.

Syntax:

plot+ geom_density_ridges(quantile_lines=TRUE, quantile_fun=function(value  ,…)mean(value))

• quantile_lines: This determines if we want a quantile line or not. It is a boolean.
• quantile_fun: It is a function that determines the position of the line.

Example:

Here, is a ridgeline plot with a mean line through it. Here, the quantile_lines parameter has been set true and in quantile_fun is the mean function with the parameter being price. This creates a line that passes through the mean price in the plot.

R

# load library ggridges and ggplot2
library(ggridges)
library(ggplot2)

# Diamonds dataset is provided by R natively
# we will use that same dataset for our plot
# basic ridgeline plot
ggplot(diamonds, aes(x = price, y = cut, fill=cut)) +

# quantile_lines and quantile_fun are used to draw a line in ridgeline plot
# quantile_lines is boolean and marks if line should be or not
# quantile_fun determines the position of line using function provided
  geom_density_ridges(quantile_lines=TRUE, quantile_fun=function(price,...)mean(price))

Output:

Here is a ridgeline plot with a line through the mean of prices of diamond of each cut. This helps us visualize the mean trend in each category of data.