August 10, 2020

Trellis Chart in Tableau

By Luke Stanke
Consider the following line chart that shows total sales by quarter over four years and is broken down by the 17 sub-categories.

Pretend you are someone in your audience for this plot. Their response will be: what the heck is this crap! It’s too messy! The reality is almost no one is going to want to see a line plot with more than three lines. Your audience wants to trace a single line and it’s impossible to follow just one of the lines in this plot–even with unique color encoding. You’ve got to find a better way to communicate this information. One way we prefer to share this information is with a small multiple or trellis chart.

Tableau’s current process for creating small multiples or trellis charts is to add a dimension to rows and a second dimension to columns. But what if you want to do it with a single dimension? This tutorial show you how?

Step 1: Build Rows and Columns

Create a calculation called [INDEX].

					// Index

Create an integer parameter and set the number of columns you would like to see. For the example we are using 5 columns. Call the parameter [Total Columns].

Now create the [Column] and [Row] placeholder calculations.

					// Column
([Index] - 1) % [Total Columns]
					// Row
(([Index] - 1) - [Column]) / [Total Columns])

For this example we’ll plot [Sub-Category]. Add [Sub-Category] and [Index] to detail. Place [Column] on columns and [Row] on rows. Make sure [Column] and [Row] are discrete dimensions. Edit the table calculations and select [Sub-Category].

From here you can make whatever visualizations you want. But for this example we’ll show sales by quarter.

Step 2: Build the Visualization

Add Quarter of Order Date to columns. Add year of Order Date to color and SUM(Sales) to rows. You will eventually replace SUM(Sales) with a different calculation.

Step 3: Add Labels Above the Bars

To add labels we need to create a calculation that will center a label above the bars. You can do this with a calculation called [Order Date | Trellis Label].

					// Order Date | Trellis Label
{MIN([Order Date])} + (({MAX([Order Date])} - {MIN([Order Date])})/2)

Add this calculation to the right of the quarter of order date calculation. Change this mark type to text. Create an additional calculation called [Bars + Label]. This calculation will “dynamically” create the appropriate aggregation based on the number of marks in a cell.

					// Bars + Label
IF SIZE() > 1 
THEN SUM([Sales]) 
ELSE 1.1 * AVG({
            {FIXED [Sub-Category], DATETRUNC("quarter", [Order Date]) : 

Replace SUM(Sales) with [Bars + Label]. Edit the table calculation of [Bars + Label] so labels are even across the top.

Add [Sub-Category], [Index] and SUM(Sales) to text on the text marks card. Sort [Sub-Category] descending by sum of sales.

Step 4: Format

I’ve added year to color on bars, but removed year from color on the text marks card. Then I formatted the bars. Finally I added max labels.

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