Polygon Waterfall Charts
Aug 8, 2019Klaus Schulte
In the past weeks, I had the immense honor to collaborate with Steve Wexler on revisiting his famous Churn Dashboard from the Big Book of Dashboards. The #BBOD was one of the first books that came across my way when I discovered dataviz and Tableau as a topic about two years ago.
My read for the Weekend. Just arrived at our library at @FHMS_Wirtschaft @acotgreave #Tableau #dashboarding pic.twitter.com/TfJPmKo4pr
— Klaus Schulte (@ProfDrKSchulte) August 11, 2017
Steve already published a blog about our collaboration and you can also explore the revisited Churn Dashboard on Tableau Public. We discussed a lot of different approaches to combine a waterfall with a line chart. Steve’s preferred solution, which he describes in the blog post, combines Gantt bars with a jump line chart.
As Steve points out, this solution works very well for several reasons:
However, there are a few use cases, where a different approach is needed:
For these use cases, I suggest using a polygon approach, which I describe below.
click to play with the interactive version on Tableau Public
This technique uses the polygon mark instead of the Gantt mark. And it includes a parameter you can use to set the bar size that fits best to your design:
The post will guide you through the steps to create this chart.
For my polygon waterfall, I need four marks for each bar and a point order to connect the marks. For the jump lines I’m using the two bottom marks from each bar.
This requires a little bit of data prep first.
While I’m able to plot several points on rows using measure values, I cannot do this for columns at the same time, because you can use Measure Value only once. Therefore, I have to bring in a second copy of the data, resulting in a new dimension [Table Name] with “unpivotet” for the first copy and “unpivotet1” for the second copy.
For my date axis, I’m using my two different kind of bars [Description] for my two left side polygon marks ([Table Name]=”unpivotet”) and my two right side polygon marks ([Table Name]=”unpivotet1″) for each month.
is a parameter to set the width of the bars.
This produces 48 marks on my x-axis, four for each month.
There is a measure [Amount] in the original data for gained and lost subscribers by month. Based on this measure, I calculate the running sum along my dates [Running Sum (Amount)] and the previous value [Lookup Running Sum (Amount)] in a first step:
As already stated, I’m using Measure Values on rows for my polygons using the following two fields to calculate my four values for each bar.
Values 1+2 are calculated with the first copy of the data (“unpivotet”) and values 3+4 with the second copy (“unpivotet1”). And each value can either be the running sum [Running Sum (Amount)] or the previous running sum [Lookup Running Sum (Amount)].
This is giving me my 96 marks, 8 for every month. (I chose the circle mark here to demonstrate this.)
For both my measures (Value 1+3 and Value 2+4), both nested table calculations have to be computed along month # (polygon), Month of Date, Description for each Table Name.
Switching the mark type to polygon and defining the path by using my measure from the x-axis produces my waterfall chart:
Like Steve did in the GANTT approach, I’m connecting the waterfall bars by using a jump line.
Therefore, I’m calculating the bottom values in a separate calculated field.
We need to make sure to compute the table calculations like shown in the screenshot:
In the last step, I’m creating a dual axis and labeling the line chart at the bottom right (“unpivotet1”) of the “Lost”-marks:
I admit, this is advanced stuff, but there might be some good use cases for this, like mentioned above.
Let’s for example have a look at the automatically generated mobile layouts:
The waterfall chart itself works without further ado, I would only get rid of the labels in the phone layout.
The one obvious disadvantage – beside the need of an extra copy of the data – is, that we cannot use a date field on columns. So, normally, you would have to bring in a second sheet to show the month names.
In this case, I used a custom format for the axis, which makes the chart obviously static here. So be careful doing this!
I hope you enjoyed reading and that you’ll find own use cases for both approaches, the Gantt approach and this POLYGON approach.