Same Period Last Year for Fiscal Week Nbr (weeks in sales table are non standard)

DAX DAX Calculations
7

Here’s a better way to solve it. Follow these three steps.

First create this measure

PY Sales Setup = 
VAR CurrentWeek = SELECTEDVALUE( Dates[Week Number] )
VAR CurrentYear = SELECTEDVALUE( Dates[Year] )

RETURN
CALCULATE( [Total Sales], FILTER( ALL( Dates ), Dates[Week Number] = CurrentWeek && Dates[Year] = CurrentYear - 1 ) )

Then this one (use this in the table)

PY Sales = 
SUMX( 
    SUMMARIZE( Dates, Dates[Year & Week], Dates[Week Number],
    "LY Sales", [PY Sales Setup] ),
        [LY Sales] )

Then to work out the change use this

Sales Chg YoY = IF( ISBLANK( [PY Sales] ), BLANK(), [Total Sales] - [PY Sales] )
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