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Creating a Basic Beeswarm Plot in Tableau

In this blog, I’m going to show you a method of creating a simplified beeswarm plot. I use the term “simplified” (or “basic”) because this method won’t provide some of the more advanced functionality provided by other methods of creating this chart. My goal, however, is to provide you with a method that allows you to create this chart with just a handful of relatively simple calculations. I’ll also discuss some of the limitations of this approach and provide you wish some alternatives for creating a more full-featured beeswarm.

What is a Beeswarm?
Before we get into the details of how to build this chart, I think it’s important to understand what it is and how it works. A beeswarm plot is a way of showing distribution of a given of a variable while also showing each individual data point. To help demonstrate the chart, let's start with a simple histogram. The following shows ages of Premier League players. The y-axis shows the number of players and the x-axis shows the ages. With this chart, we can easily see the distribution of the ages.


But what if we wish to show each player individually, while still seeing the distribution? One option would be to create separate marks for each, making it a unit histogram.


We still retain the ability to see the overall distribution of ages, but we are also able to see each player by hovering over the marks. If we now take the unit histogram and align each "stack" along a common center point, we start to see something like a beeswarm.


In fact, we might consider this a beeswarm that uses rectangular shapes. Like the unit histogram, we can still see the distribution of ages based on the various bulges within the plot. But beeswarms typically use dots, not rectangular shapes, like shown below.


The problem with this beeswarm, however, is that we see some overlapping of dots. One of the main goals of a beeswarm is to avoid this overlapping. To correct this, we could make this chart much taller or we could make the dots much smaller. But, in this case, we might be better off just rotating the chart.


This rotation gives the beeswarm a relatively tight packing of the dots.

In addition to a beeswarm showing all players in the Premier League, we can also break them down into small multiples. For example, below I’ve created separate plots for the top 10 Premier League teams of 2020.


This allows us to compare the distributions of player ages across various teams. The general shape of each plot immediately gives us some good information, such as the fact that Arsenal’s player ages a fairly evenly distributed between ages 17 and 33, while Burnley has a much higher distribution of players who are 27+.

A logical next step from here might be to turn this into a violin plot. Violin plots show the probability density of data at different values and smooth them through use of a kernel density estimator. Because of the need for such a smoothing algorithm, these aren’t easily built in Tableau, but just to demonstrate these, I used an online tool called BoxPlotR to create one:


Like the beeswarm, we can see the relatively even distribution of ages for Arsenal and the aging players of Burnley. While violins have some advantages over beeswarms (and other plots such as box plots), we do lose visibility of individual players. So, if that’s something we need to see, a beeswarm may be a good option.

How to Build One
So, let’s talk about how to build this chart. As I’ve previously noted, this is not a true beeswarm plot, but rather a simplified version that bins the data. Later in this blog, I’ll share links to techniques for creating true beeswarms in Tableau.

The data we’re using is pretty simple—it looks like this:


We’ll start by creating our bins. We can do this using Tableau’s bins functionality, but I generally prefer the BYOB technique courtesy of Joe Mako and Jonathan Drummey, as it provides more flexibility. We don’t really need that flexibility here, but we’ll use it anyway, just in case.

1. Bin
// Custom bins. Allows more flexibility than default bins.
INT([Age]/[Bin Size])*[Bin Size]-IIF([Age]<0,[Bin Size],0)

In the above, Bin Size is a parameter that allows us to set the bin size (in this example, we’re just using 1).

Next, we create a calculated field to get the number of points in each strip (each line of dots). This will allow us to then figure out the positioning of each dot so that they are center aligned.

Points in Strip
// Number of points in the "strip".
// We could fix on Bin, but excluding ID gives...
// ...us more flexibility to add dimensions to our view.
{EXCLUDE [ID]: COUNTD([ID])}

Then we create a calculated field to get us the maximum coordinate for each strip. It’s important to note here that our shared center axis will be 0 so half of the dots will have a positive coordinate and the other half will be negative.

Max Coordinate
// Highest positive coordinate. 
[2. Points in Strip]/2 - 0.5

Finally, we use INDEX() to calculate the placement of each individual dot.

Coordinate
// Coordinate for each point.
MAX([3. Max Coordinate]) - INDEX() + 1

We wish to create a beeswarm with age on the vertical (y) axis, so we’ll drop 1. Bin on the rows shelf. It’s possible, at this point, that Tableau will interpret this as a measure and try to aggregate it. If so, right-click the pill and change it to a dimension. Then we drop ID on the detail card so we get a mark for each player. Finally, we drop 4. Coordinate on the columns shelf; once there, we right-click the pill and edit the table calculation, setting it to compute like this:


One of the keys here is that we set it to restart on every bin—essentially causing it to restart counting at 1 each time.

If you’ve done everything correctly, you’ll have a simplified beeswarm that looks exactly like the one I shared earlier.


Why & When to Use a Beeswarm
One question you might be asking is why and when might we use this type of chart. It really isn’t much different than our unit histogram, which is much easier to build, so why choose a beeswarm? That’s a great question and it reveals one of the key flaws of the simplified approach I’ve shared here. The key difference between a unit histogram and a beeswarm (other than the alignment of the data points) is that beeswarms typically do not bin the data, as I’ve done here. They typically show the actual value of the data point. So, the result of a beeswarm is generally not a set of straight horizontal lines, but lines that curve slightly as you move towards the ends.

Example beeswarm from EDU Pristine’s How to create a Beeswarm Plot in R

That said, I personally find this type of beeswarm to be difficult to understand. The lack of consistency in the placement of the dots, to me, creates a sort of visual clutter that makes it hard for me to tell what’s going on. And I question whether or not showing the actual value gives us that much additional information than what we get from binning the data. In many cases, I think a binned version of the chart is more effective.

All this being said, the question remains—when and why would we use this simplified beeswarm? And that’s a great question. In most cases, I think that a unit histogram is probably easier to read and understand, but the beeswarm does provide a viable alternative that could be very effective in some situations. The key, as always, is to understand your data, the target audience, and the questions you’re trying to answer. If, after carefully considering these three things, you find that this simplified beeswarm is viable chart, then now you know how to create it!

Alternative Approaches
There may come a time when you need a more full-fledged beeswarm plot without the limitations of this simplified approach. In that case, you are in luck! There are a few different methods for creating full-blown beeswarm plots in Tableau.

R + Tableau
R has a few different packages that allow you create beeswarms. In his blog, Beeswarm Chart in Tableau … via R, Dorian Banutoiu details how he leveraged these packages to create the coordinates need to plot a beeswarm in Tableau.

Pure Tableau
If you’ve ever seen the work of Rody Zakovich, you know that he’s a genius. He is able to make Tableau do things that I would’ve never thought possible. In his blog, Automatic Bins and Beeswarms in Tableau, Rody details a method for creating beeswarm plots 100% in Tableau. This approach is pure genius, so it’s definitely worth checking out.

Extensions
One final method is extensions. Zen Master, Chris DeMartini has done some amazing work leveraging Elijah Meek’s Semiotic to create a variety of charts, including beeswarms. His extensions can be found on the Tableau Community Extensions Page.


Ken Flerlage, November 9, 2020


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