Period over Period Change Measure

dkay84_PowerBI

having this sample table:

year and week are calculated columns

create a measure:

Delta% =
VAR yearselected =
    VALUES ( Table1[Year] )
VAR weekselected =
    VALUES ( Table1[Week] )
VAR delta =
    DIVIDE (
        CALCULATE ( SUM ( Table1[Sales] ) ),
        CALCULATE (
            SUM ( Table1[Sales] ),
            FILTER (
                ALL ( Table1 ),
                Table1[Year]
                    = yearselected - 1
                    && Table1[Week] = weekselected
            )
        )
    )
RETURN
    IF ( delta <> BLANK (), delta - 1, BLANK () )

I am not getting your solution to work with just the week number slicer.  However, since in this case there will always just be current and previous year, I changed the code to the following and it works:

Delta% = 
VAR yearselected =
    MIN(Table[Year])
VAR weekselected =
    VALUES ( Table[Week#] )
VAR delta =
    DIVIDE (
        CALCULATE ( SUM (Table[Sales] ) ),
        CALCULATE (
            SUM ( Table[Sales]  ),
            FILTER (
                ALL ( Table ),
                Table[Year]
                    = yearselected
                    && Table[Week#] = weekselected
            )
        )
    ) - 1
RETURN
    IF ( delta <> BLANK (), delta - 1, BLANK () )

The red code is where I adjusted