DAX Function to Count Days Between Start and End Dates

This document outlines the creation of a DAX function that calculates the total number of days between start and end dates in Table A. The result is then listed for each entry in the off dates column of Table B.

Overview

• Input Tables:

  • Table A: Contains Start Date and End Date.
  • Table B: Contains off dates.

• Objective: Calculate the total number of days within each date range defined in Table A and relate that count to each off date in Table B.

DAX Code

Below is a DAX code snippet for the specified functionality:

Days Counted = 
VAR OffDates = SELECTCOLUMNS(TableB, "OffDate", TableB[OffDate])
VAR Results =
    ADDCOLUMNS(
        OffDates,
        "DaysCounted",
        COUNTROWS(
            FILTER(
                TableA,
                TableA[Start Date] <= [OffDate] && 
                TableA[End Date] >= [OffDate]
            )
        )
    )
RETURN
    Results

Explanation of the Code

1. Variable Declaration:

   • OffDates: Extracts the off dates from Table B using SELECTCOLUMNS.

2. Add Columns:

   • ADDCOLUMNS: A function to add a new column to the filtered table (OffDates) where each OffDate is evaluated.

3. Counting Days:

   • COUNTROWS(FILTER(...)): For each OffDate, it counts how many rows exist in Table A where Start Date is less than or equal to OffDate and End Date is greater than or equal to OffDate.

4. Return Results:

   • The function returns the results with OffDate and the computed DaysCounted.

Input Validation

In DAX, data validation is usually handled by the data model and type enforcement in Power BI. Ensure that:

• Start Date and End Date are in date format.
• Off Date in Table B is also properly formatted.

Usage Example

To use this DAX function in a Power BI model, follow these steps:

1. Create a calculated table to store the results:

   • Navigate to the modeling tab in Power BI.
   • Use the DAX code above to define a new calculated table.

2. You can also visualize the results using a table visual:

   • Add the OffDate and DaysCounted from the newly created calculated table to your report.

Conclusion

This DAX function efficiently counts the number of days between start and end dates from Table A and relates the results to each off date in Table B. With its structured approach and inclusion of necessary variables, the function adheres to best practices ensuring scalability and clarity.

For further learning on advanced DAX and data manipulation, consider exploring resources available on the Enterprise DNA Platform.