Ridgeline plot in ggplot2 with ggridges

Package

Author

Claus O. Wilke

Sample data

For this tutorial we are going to use a subset of the diamonds data set from ggplot2 package.

# install.packages("ggplot2")
library(ggplot2)

# Sample data
df <- diamonds[1:100, c("color", "depth")]

Ridgeline plots (joy plots) with `geom_density_ridges`

The geom_density_ridges function from the ggridges package allows creating a ridgeline visualization. Given a numerical variable (depth) and a categorical variable (color) a density estimation of the data will be calculated and displayed for each group.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  geom_density_ridges()

Basic ridgeline plot in ggplot2

geom_density_ridges2

Note that there is an equivalent function named geom_density_ridges2 which uses closed polygons to display the density estimates, so the line will also appear at the bottom of each density estimation.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  geom_density_ridges2()

The geom_density_ridges2 function

Cut the trailing tails

The rel_min_height argument of the function can be used to cut the trailing tails. You will need to fine tune the value depending on your data.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  geom_density_ridges(rel_min_height = 0.005)

Cut the trailing tails of the ridgeline plot in ggplot2

Scale

In addition, the scale argument controls the scaling of the ridgelines relative to the spacing between them.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  geom_density_ridges(scale = 3)

Change the scale of the density ridges in ggplot2

Alternative stats

The stat argument can be used to select the statistical transformation to be used.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  geom_density_ridges(stat = "binline",
                      bins = 20, draw_baseline = FALSE)

Ridgeline binline

Color customization

Ridgeline plot with the geom_density_ridges function of ggridges

Fill color and transparency

The default gray color of the ridgelines can be changed with the fill argument of the geom_density_ridges function. Note that you can also specify a level of transparency with alpha.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  geom_density_ridges(fill = "lightblue", alpha = 0.5)

Color of the lines of the densities of a ridgeline plot

Border color

The color argument of the function controls the color of the lines. As in other plots you can also change the line type and the width of the lines.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  geom_density_ridges(fill = "white",
                      color = 4,
                      linetype = 1,
                      lwd = 0.5)

Fill the color of the ridgeline densities by group

Color based on group

You can also fill the densities based on the categorical variable, passing it to the fill argument of aes. The color palette can be changed with scale_fill_manual, for instance.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color, fill = color)) +
  geom_density_ridges()

Cyclical colors in ggridges with scale_fill_cyclical and scale_color_cyclical

Cyclical color scales

The scale_fill_cyclical and scale_color_cyclical functions can be used to add cyclical fill and border colors to the density estimations.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color, fill = color, color = color)) +
  geom_density_ridges() +
  scale_fill_cyclical(name = "Cycle", guide = "legend",
                      values = c("#99E6FF", "#4CA6FF")) +
  scale_color_cyclical(name = "Cycle", guide = "legend",
                       values = c(1, 4))

Filling the ridgelines with a gradient color using ggridges

Gradient

You can pass stat(x) or factor(stat(x)) to the fill argument of aes and use geom_density_ridges_gradient and a continuous fill color scale to fill each ridgeline with a gradient.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color, fill = stat(x))) +
  geom_density_ridges_gradient() +
  scale_fill_viridis_c(name = "Depth", option = "C")

Change the theme of the rigeline plot in ggplot2

Change the theme

Note that you can also change the ggplot2 theme to modify the appearance of the plot. The ggridges package provides the theme_ridges theme.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color, fill = stat(x))) +
  geom_density_ridges_gradient() +
  scale_fill_viridis_c(name = "Depth", option = "C") +
  coord_cartesian(clip = "off") + # To avoid cut off
  theme_minimal()

Adding quantiles and probabilities with `stat_density_ridges`

If you use stat_density_ridges instead of geom_density_ridges and set the quantile_lines argument to TRUE the quantiles will be calculated and displayed for each density.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  stat_density_ridges(quantile_lines = TRUE, alpha = 0.75)

Adding quantiles to the ggplot2 ridgelines

Number of quantiles

The quantiles argument controls which or how how many quantiles are displayed. If you pass an integer the data will be cut into that many equal quantiles.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  stat_density_ridges(quantile_lines = TRUE, alpha = 0.75,
                      quantiles = 2)

Using the stat_density_ridges function from ggridges

Specify the quantiles

If you pass a value or a vector of values between 0 and 1 to the quantiles argument those quantiles will be calculated and displayed.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color)) +
  stat_density_ridges(quantile_lines = TRUE, alpha = 0.75,
                      quantiles = c(0.05, 0.5, 0.95))

Specify which quantiles to show on the ridgeline

Color by quantile

Passing stat(quantile) to fill and setting calc_ecdf and geom = "density_ridges_gradient" each quantiles will be filled with a different color. Note that if you set quantile_lines = TRUE the vertical lines for each quantile will be drawn.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color, fill = stat(quantile))) +
  stat_density_ridges(quantile_lines = FALSE,
                      calc_ecdf = TRUE,
                      geom = "density_ridges_gradient") +
  scale_fill_brewer(name = "")

Filling colors for the quantiles with calc_ecdf

Highlight the tails of the distribution

The same approach described above can be used to highlight the tails of the distributions.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = depth, y = color, fill = stat(quantile))) +
  stat_density_ridges(quantile_lines = TRUE,
                      calc_ecdf = TRUE,
                      geom = "density_ridges_gradient",
                      quantiles = c(0.05, 0.95)) +
  scale_fill_manual(name = "Prob.", values = c("#E2FFF2", "white", "#B0E0E6"),
                    labels = c("(0, 5%]", "(5%, 95%]", "(95%, 1]"))

Highlighting the tails of the rigeline distributions

Mapping the tails probabilities onto color

Similarly, using stat(ecdf) it is possible to add a gradient to the densities displaying the tail probabilities.

# install.packages("ggridges")
library(ggridges)
# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(depth, y = color,
               fill = 0.5 - abs(0.5 - stat(ecdf)))) +
  stat_density_ridges(geom = "density_ridges_gradient", calc_ecdf = TRUE) +
  scale_fill_gradient(low = "white", high = "#87CEFF",
                      name = "Tail prob.")

Mapping the tails probabilities onto color with ggridges