DAX Function to Compute Sum for the First 4 Ranks

Overview

This document outlines a DAX function designed to compute the sum of the Cost column from the Goods table, considering only the first four ranks identified using the RANKX function. The solution ensures that grand totals are handled correctly.

Key Points

• Functionality: Sum the Cost of the top four goods based on their ranking.
• Ranking Logic: Use RANKX to establish ranks without an explicit ranking column.
• Grand Total Handling: Ensure that grand totals are accurate and consistent with the first four ranks.

DAX Code

SumFirstFourRanks = 
VAR RankedGoods =
    ADDCOLUMNS(
        Goods,
        "Rank", RANKX(Goods, Goods[Cost], , DESC, DENSE)
    )
VAR TopFourCosts =
    FILTER(
        RankedGoods,
        [Rank] <= 4
    )
RETURN
    SUMX(TopFourCosts, Goods[Cost])

Code Explanation

1. Calculate Rank:

   • ADDCOLUMNS is used to add a new calculated column "Rank" to the Goods table.
   • RANKX ranks each Good item based on its Cost in descending order using DENSE ranking.

2. Filter for Top 4:

   • FILTER creates a new table holding only those goods with a rank of 4 or less.

3. Calculate Sum:

   • SUMX iterates through the filtered table (TopFourCosts) to compute the total Cost of those items.

Grand Total Handling

In Power BI, the measure will automatically handle grand totals based on the context provided by the visualizations. The grand total will reflect the total sum of all items, but the measure itself focuses on the first four ranks.

Example Usage

To use this measure in a Power BI report:

1. Add the SumFirstFourRanks measure to your visualizations, such as tables or cards.
2. Ensure that your Goods table is present in the report model.
3. This will display the sum of the costs of the top four products based on their costs, maintaining accurate totals for different contexts.

Conclusion

The provided DAX function efficiently sums the costs of the top four ranked goods without requiring a fixed ranking column. It follows best practices in handling calculations and ensures that results are presented clearly, adaptable to various reporting contexts. For further learning and advanced techniques in DAX, consider exploring the Enterprise DNA Platform.