Adding Marginal Density Plots to a Graph in R

In this video I demonstrate how to add marginal density plots to your ggplot2 scatterplots in R using two different R packages – ggExtra and ggside. Using these packages I will show you how to add density curves, histograms, boxplots, and violin plots for the marginal distributions and how to divide them by different categories.

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library(tidyverse)

## ggExtra #######
library(ggExtra)

# basic scatterplot and marginal distributions 
iris.scatter.1<-ggplot(iris, aes(Sepal.Length, Sepal.Width)) +
  geom_point()
iris.scatter.1
ggMarginal(iris.scatter.1)
ggMarginal(iris.scatter.1,type="histogram")
ggMarginal(iris.scatter.1,type="densigram")
ggMarginal(iris.scatter.1,type="boxplot")
ggMarginal(iris.scatter.1,type="violin")

# coloured by species
iris.scatter.2 <- ggplot(iris, aes(Sepal.Length, Sepal.Width, colour = Species)) +
  geom_point() + theme(legend.position="bottom")
iris.scatter.2
ggMarginal(iris.scatter.2, groupColour = TRUE, groupFill = TRUE) 
ggMarginal(iris.scatter.2, groupColour = TRUE, groupFill = TRUE, type="histogram")
ggMarginal(iris.scatter.2, groupColour = TRUE, groupFill = TRUE, type="densigram")
ggMarginal(iris.scatter.2, groupColour = TRUE, groupFill = TRUE, type="boxplot")
ggMarginal(iris.scatter.2, groupColour = TRUE, groupFill = TRUE, type="violin")


## ggside
library(ggside)

# marginal densities
i2 <- iris %>%
  mutate(Species2 = rep(c("A","B"), 75))
p <- ggplot(i2, aes(Sepal.Width, Sepal.Length, color = Species)) +
  geom_point()
p2 <- p + geom_xsidedensity(aes(y=stat(density))) +
  geom_ysidedensity(aes(x=stat(density))) +
  theme_bw()
p2 + labs(title = "No Facets")

# facet across two category combinations
p2 + facet_grid(Species~Species2, space = "free", scale = "free_y") 

# boxplot and density 
ggplot(mpg, aes(displ, hwy, colour = class)) + 
  geom_point(size = 2) +
  geom_xsideboxplot(aes(y =class), orientation = "y") +
  geom_ysidedensity(aes(x = after_stat(density)), position = "stack") +
  theme(ggside.panel.scale = .3) +
  scale_xsidey_discrete() +
  scale_ysidex_continuous(guide = guide_axis(angle = 90), minor_breaks = NULL)