DAX Function to Return Dates for Previous Year

Overview

The following DAX function generates a table containing all dates from the previous year up until today. This is useful for time series analysis and reporting where you need to compare data from the previous year to current performance metrics.

Function Definition

PrevYearDates = 
VAR TodayDate = TODAY()  // Get the current date
VAR StartDate = EDATE(TodayDate, -12)  // Calculate the first day of the previous year
RETURN
    FILTER(
        CALENDAR(StartDate, TodayDate),  // Create a calendar from the start of the previous year to today
        [Date] <= TodayDate  // Ensure the filter only includes dates up to today
    )

Explanation of Code Elements

1. Variables:

   • TodayDate: Holds the current date using the TODAY() function.
   • StartDate: Calculates the same date last year using EDATE() to shift the current date by -12 months.

2. CALENDAR Function:

   • Generates a continuous table of dates starting from StartDate to TodayDate.

3. FILTER Function:

   • Filters out the generated dates to include only those up to the current date.

Key Points

• The function dynamically adjusts based on the current date, providing the right range of dates each time.
• It leverages DAX functions for efficient date management and filtering.

Usage Example

Suppose you want to create a visual that compares sales data from the previous year with the current year. You can create a table in your Power BI model using this DAX code.

This PrevYearDates table can be linked with your sales data by date to analyze trends over the past two years, enhancing your reporting capabilities and insights.

Summary

This DAX function efficiently creates a date table for the previous year up until today, streamlining comparative analyses and making your data visualization more comprehensive. For more advanced learning on DAX and Power BI, consider exploring resources offered at the Enterprise DNA Platform.