Published: 08 Dec 2023 Last Modified Date: 08 Dec 2023
Question
How to create a trend line for a discrete Date axis.
It is possible to use a trend line when using the continuous date in the x-axis.
But, if you are using a discrete date field in the x-axis, the Trend Line function is greyed out.
Environment
Tableau Desktop
Answer
Use a table calculation to manually create a trend line and use the dual-axis function to merge with the original graph.
Follow along with the sample packaged workbook found in the Attachments section of this article to review the steps below.
1. Create a slope calculation for the trend line with the date. [Sales] is the y-axis Field name: 1. slope Calculation: WINDOW_COVAR(INDEX(), SUM([Sales])) / WINDOW_VAR(INDEX())
2. Create a slope calculation for the trend line with the date. Field name: 2. Intercept Calculation: WINDOW_AVG(SUM([Sales])) - [1. slope] * WINDOW_AVG(INDEX())
3. Create a trend line calculation. Field name: 3. trend line Calculation: INDEX()*[1. slope]+[2. Intercept]
4. Add the [3. trend line] in the [Rows] shelf and set as the dual axis. Synchronize the trend line axis.