Level of Detail (LOD) Expressions in Tableau allow you to compute values at different levels of granularity in your data without affecting the overall aggregation. Fixed LOD expressions specifically enable you to fix a specific dimension's level while aggregating or computing a measure for another dimension. Let's go through a step-by-step tutorial with examples:
Example Data: Let's consider a dataset of sales transactions with the following columns: Order ID, Product, Category, Sales, Profit, and Region.
Tutorial: Using Fixed Level of Detail (LOD) Expressions in Tableau
Step 1: Open Tableau and Connect to Your Data
Launch Tableau and connect to your dataset (e.g., Excel, CSV, database).
Step 2: Create a Simple Visualization
Drag the Category dimension to Rows and the Sales measure to Columns to create a bar chart showing total sales by category.
Step 3: Create a Fixed LOD Expression
Right-click anywhere on a blank area in the calculated field pane and select "Create Calculated Field."
To create a Fixed LOD expression, use the {FIXED} keyword followed by a specific dimension to fix the level of detail. For example, let's create an LOD expression to calculate the total sales for each category within a specific region:
{FIXED [Region] : SUM([Sales])}
This expression tells Tableau to calculate the sum of sales for each category while fixing the level of detail at the region level.
Step 4: Use the Fixed LOD Expression in a Visualization
Drag the Fixed LOD expression you created (e.g., {FIXED [Region] : SUM([Sales])}) to the Rows shelf alongside the Category dimension.
This will create a visualization that shows the total sales for each category within each region.
Step 5: Customize Your Visualization
You can further customize your visualization by adding labels, colors, or other dimensions to enhance the presentation of the data.
Step 6: Understand the Results
Analyze the visualization. You will see that the total sales for each category are calculated within each region, thanks to the Fixed LOD expression. This means the aggregation is done at the region level, even though you're displaying data by category.
Step 7: Create Additional Fixed LOD Expressions
You can create more Fixed LOD expressions as needed to perform calculations at various fixed levels of detail in your data. For example, you could calculate profit margins for products within a fixed region.
Step 8: Save and Share Your Workbook
Once you're satisfied with your visualization, save your Tableau workbook and share it with others as needed.
That's it! You've created a Fixed Level of Detail (LOD) expression in Tableau to perform calculations at a specific level of detail while visualizing your data at a different level. Fixed LOD expressions are powerful tools for analyzing data with complex hierarchical structures or when you need to perform calculations that are not affected by changes in the visualization's granularity.
