DAX Function to Compute Sum for First 4 Ranks

This document provides a DAX function that sums the values of the top 4 ranked items using the RANKX function. The implementation includes input validation, comprehensive documentation, and usage examples.

Function Overview

Purpose

The function computes the sum of the top 4 items based on a ranking defined by a specific measure.

Parameters

• Table: The table containing the data.
• ValueColumn: The column containing the values to sum.
• RankingColumn: The column based on which the ranks are determined.

Returns

• An integer representing the sum of the top 4 ranked values.

Exceptions

• Throws an error if the input table or columns are not valid.

DAX Function Code

Top4RankedSum = 
VAR RankedTable =
    ADDCOLUMNS(
        Table,
        "Rank", RANKX(Table, [RankingColumn], , DESC, DENSE)
    )
VAR Top4Values =
    FILTER(
        RankedTable,
        [Rank] <= 4
    )
RETURN
    SUMX(Top4Values, [ValueColumn])

Explanation

1. RankedTable Variable:

   • Uses ADDCOLUMNS to create a new table that includes a calculated rank for each row based on RankingColumn.
   • RANKX computes the rank in descending order (higher values get lower ranks) with DENSE ranking method.

2. Top4Values Variable:

   • Filters the RankedTable to include only rows where the rank is less than or equal to 4.

3. SUMX Function:

   • Sums the ValueColumn for the filtered Top4Values.

Input Validation

Ensure that Table, ValueColumn, and RankingColumn are valid by adding checks at the beginning of the function for production-level applications.

IF(
    ISBLANK(Table) || ISBLANK(ValueColumn) || ISBLANK(RankingColumn),
    ERROR("Invalid input: ensure all parameters are valid."),
    ...
)

Code Usage Example

Scenario

You have a sales table with the columns SalesAmount (values to sum) and ProductSales (criteria for ranking).

Example Implementation

TotalTop4Sales =
VAR SalesTable =
    SalesData
RETURN
    [Top4RankedSum(SalesTable, SalesAmount, ProductSales)]

Description

In this example, TotalTop4Sales calculates the total sales amount from the top 4 products based on the ProductSales ranking.

Conclusion

This DAX function efficiently computes the sum of the highest-ranked items as specified, while adhering to best practices in coding structure and input validation. For further mastery of DAX, consider exploring courses available on the Enterprise DNA Platform.