ggforce: Make a Hull Plot to Visualize Clusters in ggplot2
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The ggforce
package is a ggplot2
extension that adds many exploratory data analysis features. In this tutorial, we’ll learn how to make hull plots for visualizing clusters or groups within our data.
RTips Weekly
This article is part of RTips Weekly, a weekly video tutorial that shows you stepbystep how to do common R coding tasks.
Here are the links to get set up. ?
Video Tutorial
Follow along with our Full YouTube Video Tutorial.
Learn how to use ggforce
in our 7minute YouTube video tutorial.
What is a Hull Plot?
The Hull Plot is a visualization that produces a shaded areas around clusters (groups) within our data. It gets the name because of the Convex Hull shape. It’s a great way to show customer segments, group membership, and clusters on a Scatter Plot.
Hull Plot (We’ll make in this tutorial)
We’ll go through a short tutorial to get you up and running with ggforce
to make a hull plot.
Hull plots with ggforce
[Tutorial]
This tutorial showcases the awesome power of ggforce
for visualizing distributions.
Tutorial Credits
This tutorial wouldn’t be possible without the excellent work of Thomas Lin Pedersen, creator of ggforce
. Check out the ggforce package here.
Before we get started, get the R Cheat Sheet
ggforce
is great for extending ggplot2 with advanced features. But, you’ll need to learn ggplot2
to take full advantage. For these topics, I’ll use the Ultimate R Cheat Sheet to refer to ggplot2
code in my workflow.
Quick Example:
Download the Ultimate R Cheat Sheet. Then Click the “CS” hyperlink to “ggplot2”.
Now you’re ready to quickly reference the ggplot2
cheat sheet. This shows you the core plotting functions available in the ggplot library.
Onto the tutorial.
Load the Libraries and Data
First, run this code to:
 Load Libraries: Load
ggforce
,tidyquant
, andtidyverse
.  Import Data: We’re using the
mpg
dataset that comes withggplot2
.
Here’s the mpg
dataset. We’ll focus on “hwy” (fuel economy in Miles Per Gallon), “displ” (engine displacement volume in liters), and “cyl” (number of engine cylinders).
hull plot: Using ggplot
Next, we’ll make a hull plot that highlights the Vehicle Fuel Economy (MPG) for Engine Size (Number of Cylinders and Engine Displacement). It helps if you have ggplot2
visualization experience. If you are interested in learning ggplot2
indepth, check out our R for Business Analysis Course (DS4B 101R) that contains over 30hours of video lessons on learning R for data analysis.
Step 1: Make the Base Scatter Plot
The first step is to make the scatter plot using ggplot2
. We:

Prep the Data: Using
mutate()
to add a descriptive Engine Size column that will display the Number of Cylinders. 
Map the columns: Using
ggplot()
, we map the displ and hwy column. 
Make the scatter points: Using
geom_point()
, we add scatter plot points to our base plot. Refer to the Ultimate R Cheat Sheet and ggplot2 “CS” for more geoms.
This produces our base plot, which is a scatter plot of displacement vs highway fuel economy.
Step 2: Add the Hull Plot with geom_mark_hull()
Next, we add our hull plot geometry layer using ggforce::geom_mark_hull()
. This produces the hull plot shaded regions indicating the groups. We map the descriptive engine size column to the fill
and label
aesthetics. We adjust the concavity
to smooth out the concavity.
And here’s the output. We can see that the hull plot shows the cylinder class membership for the vehicles scatter points.
Step 3: Make the plot look professional
It’s a good idea to spruce up our plot, especially if we are going to present to business stakeholders in a presentation or report. We’ll leverage tidyquant
and ggplot
for theme customization. Refer to the Ultimate R Cheat Sheet and ggplot2
documentation for more customizations.
And here’s the output. We have our final plot that tells the story of how highway fuel economy varies with the vehicle’s number of cylinders and engine displacement volume.
Summary
We learned how to make hull plots with ggforce
. But, there’s a lot more to visualization.
It’s critical to learn how to visualize with ggplot2
, which is the premier framework for data visualization in R.
If you’d like to learn ggplot2
, data visualizations, and data science for business with R, then read on. ?
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