In Power BI, effectively ranking data is crucial for insightful analysis. Two primary DAX functions facilitate this: TOPN and RANKX. While both serve to rank data, they operate differently and are suited for distinct scenarios.

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Understanding RANKX vs. TOPN in Power BI

Before diving into the how-to, it’s important to understand the core difference between RANKX and TOPN.

Feature	RANKX	TOPN
Type	Scalar function – returns a rank per row	Table function – returns a filtered table
Context Aware	Yes – respects row context, slicers, and filters	No – must be wrapped in CALCULATE to be dynamic
Output	A rank number per item	A filtered list of top N rows
Use Case	Dynamic, filter-sensitive ranking for reports	Static or quick top N table creation
Typical Scenario	Visual ranking with slicers (Top 10 customers by region)	Show top N products in a measure or KPI

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Step-by-Step: Building Dynamic Top N Ranking with RANKX

Step 1: Create a Sales Measure

Total Sales = SUM('Orders'[Sales])

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Step 2: Create a What-If Parameter for N

Go to Modeling > New Parameter:

• Name: TopNSelector
• Data Type: Whole Number
• Min: 1, Max: 20, Increment: 1
• Default: 5

This creates a slicer that lets users control the N in “Top N.”

Step 3: Create a Dynamic Rank Measure

Create the RANKX Measure

Customer Rank = 
RANKX(
    ALL('Customers'[Customer Name]),        -- Ranks all customers, ignoring filters
    CALCULATE([Total Sales]),               -- Evaluate Total Sales for each
    , 
    DESC, 
    Dense
)

Use CALCULATE to ensure proper evaluation within RANKX.
Without ALL(...), each row may see itself only—causing all ranks to return 1.

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Optional: Respect Filters with ALLSELECTED

If you’d like the ranking to adjust based on filters (like Region):

Customer Rank = 
RANKX(
    ALLSELECTED('Customers'[Customer Name]), 
    CALCULATE([Total Sales]), 
    , 
    DESC, 
    Dense
)

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Step 4: Create a Flag to Filter Top N

Top N Customer Flag = 
IF(
    [Customer Rank] <= SELECTEDVALUE('TopNSelector'[TopNSelector]), 
    1, 
    0
)

Use this flag to control which rows appear in your visual.

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Step 5: Build the Table Visual

In a table visual, add:

• Customer Name
• [Total Sales]
• [Customer Rank]

Apply a visual-level filter:

• Filter on Top N Customer Flag = 1

Place the TopNSelector slicer on the page to let users pick their desired Top N.

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When to Use TOPN vs. RANKX

• Use TOPN: For simple, static rankings where filter context isn’t a concern. It’s quick and easy for straightforward top N.
• Use RANKX: When you need dynamic rankings that adjust based on user interactions, slicers, or filters. It provides more flexibility and accuracy in interactive reports.

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Additional Tips

• Handling Ties: The Dense parameter in RANKX ensures that tied values receive the same rank, and the next rank is the subsequent integer.
• Filter Context: Be cautious with filter contexts. Using ALL removes filters from the specified table, while ALLEXCEPT retains filters on specified columns.
• Performance: For large datasets, be mindful of performance implications when using these functions, especially within complex measures or visuals.

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By understanding and appropriately applying TOPN and RANKX, you can create dynamic, responsive reports in Power BI that provide valuable insights tailored to user interactions.