Do you know the same period last year in powerbi

Year on year is the most basic index in the analysis index , But you really know PowerBI Year on year implementation ？

Let's first look at the common way we write year-on-year

sales = SUM( 'FactSales'[sales] )

sales.PY = 
CALCULATE(
    [sales],
    DATEADD( 'DimDate'[Date], -1, YEAR )
)

sales.PY2 = 
CALCULATE(
    [sales],
    SAMEPERIODLASTYEAR( 'DimDate'[Date] )
)

Whether to use DATEADD still SAMEPERIODLASTYEAR Can achieve year-on-year calculation ,

As shown in the above figure , There seems to be no problem , But when we refine the granularity to days, we will look at the data ,2022 year 7 Monthly data only 24 Number , However, the above two methods calculate the month dimension and the year-on-year dimension 2021 year 7 The whole month .

At this time, many people may think that the monthly to date calculation will be correct , Is that right , Let's take a look

sales.MTD = TOTALMTD( [sales], 'DimDate'[Date] )

sales.MTD.PY = 
CALCULATE(
    [sales.MTD],
    DATEADD(DimDate[Date], -1, YEAR )
)

You will find that even if we use MTD To calculate the same period last year , However, in the monthly dimension, the data of the whole month of last year is still calculated , If you look at the data carefully, you will find that you only need to calculate the same period last year if it does not happen in the current period , It doesn't count , That is, the current data only arrive 2022.7.24, So when calculating the same period last year, you only need to calculate 2021.7.24 that will do .

sales.PY3 = 
VAR maxdate =
    CALCULATE (
        LASTNONBLANK ( 'DimDate'[Date], [sales] ),
        ALL ( 'DimDate'[Date] )
    )
RETURN
    CALCULATE (
        [sales],
        SAMEPERIODLASTYEAR (
            FILTER ( VALUES ( 'DimDate'[Date] ), 'DimDate'[Date] <= maxdate )
        )
    )

It can be seen that in the month dimension, the same period last year only calculated 2021.7.24, And the value is no longer displayed on the date that does not occur in the current year .

But there will also be special circumstances , such as 2020 year 2 Month is a leap month 29 God ,2021 year 2 Month only 28 God , So it's calculating 2021.2 In the same period last year, it will still be calculated 2020.2 Monthly data , That is, calculate to 2020.2.29, But this is exactly what we need .