DAX Function for Year-to-Date (YTD) Calculation for Previous Year

This section details a DAX function to calculate the Year-to-Date (YTD) values for the year prior to a selected year in a slicer. The function will provide insights into the performance of the previous year relative to the current selection.

Function Overview

Purpose

To calculate the YTD for the year preceding the selected year in a Year slicer.

Parameters

• Year Slicer: A single-value slicer that a user can select a specific year from.

Returns

• YTD total for the previous year based on the date context set by the slicer.

Code Implementation

The following DAX code snippet achieves the YTD calculation for the previous year.

PreviousYTD =
VAR SelectedYear = SELECTEDVALUE('Date'[Year])  // Get the year selected by the user
VAR PreviousYear = SelectedYear - 1               // Calculate the previous year
RETURN
    CALCULATE(
        TOTALYTD(
            SUM('Sales'[Amount]),                 // Replace 'Sales'[Amount] with the relevant measure
            'Date'[Date],                        // The date table must have a continuous date column
            "12/31"                              // Year-end date
        ),
        'Date'[Year] = PreviousYear              // Filter the results to the previous year
    )

Explanation of the Code

• Variable Declaration:

  • SelectedYear: Captures the year from the slicer.
  • PreviousYear: Derives the previous year from the SelectedYear.

• CALCULATE Function:

  • This function modifies the filter context to compute the YTD value for a specific year.

• TOTALYTD Function:

  • Computes the total up to the last date of the year in the specified context.
  • Aggregates data from the 'Sales' table using the specified measure (in this case, 'Sales'[Amount]).

• Date Filter:

  • Ensures that the calculation only considers data from the previous year.

Input Validation

• The script assumes that the 'Date' table is well-constructed with a continuous date range. Ensure that there are no gaps in dates.
• A check can be implemented to confirm that a valid year is selected if necessary.

Example of Usage

To use this function:

1. Incorporate the DAX measure into your Power BI report.
2. Create a slicer visual using the 'Date'[Year] field.
3. Observe the results as the slicer changes, reflecting the YTD values for the previous year dynamically.

Conclusion

This DAX function effectively encapsulates the required logic for calculating and displaying Year-to-Date values for the previous year, enriching your reporting capabilities. For advanced DAX techniques, consider exploring courses available on the Enterprise DNA Platform.