In this Tableau data visualization tutorial, we’ll learn to use the LOOKUP table calculation function to return sales revenue for the same day last year. A number of different techniques are used in the creation of this dashboard.
I designed this dashboard solely as a teaching exercise to help you understand the LOOKUP function and how to show the same date last year in a separate column.
- As we learned in a previous video Tableau Table Calculations Simplified, (make sure to watch this video afterwards for more clarity), we’ll compute using specific dimensions and then use “At the level” to make sure our LOOKUP table calculation is performing correctly.
- The “Show Missing Values” option is selected to fill in date gaps in the data set that do not exist. Ensuring 365 dates per year are present in the visualization enables the offset (i.e., -1) in the LOOKUP calculation to arrive at correct sales revenue from the same day in the previous year.
- You’ll learn that we can filter on a table calculation by using another table calculation. Filters based on table calculations do not filter out underlying data. Instead, the data is hidden from the view, allowing dimension members to be hidden from the view without impacting the data in the view.
Observe the Tableau filter order of operations above. Applying a dimension filter before the Table Calculation filter removes underlying data which affects the proper functioning of Table calculations. Typically, Table Calculations only work on values that are visible in the view. By applying a table calculation (which is last in the order of operations) you preserve underlying data but filter out data from the view.
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