Last Week Value

Hi, Lucy_Ramirez 

Accordin to your description, you want to get the last week value by the "Year and week". 

Here are the steps you can refer to :
(1)This is my test data:

(2)We need to create a 'Date' table as a dimension table:

Date = ADDCOLUMNS( 
CALENDAR(FIRSTDATE('Table'[Date]),LASTDATE('Table'[Date])),
"Year", YEAR([Date]),
"Week", weeknum([Date]),
"Year_Week", year([Date]) * 100 + weeknum([Date])
)

The relationship is as belows:

(3)Then i create a measure to sum of the value like you:

FinalInventory = SUM('Table'[Value])

(4)Then we can create a measure like this:

Last Week = var _curyearweek = MAX('Date'[Year_Week])
var _t = SUMMARIZE(ALLSELECTED('Date') , 'Date'[Year_Week] ,"Value" , [FinalInventory])
var _maxyearweek =MAXX( FILTER( _t , [Year_Week] <_curyearweek) , [Year_Week])
var _t2 = FILTER(_t, [Year_Week]=_maxyearweek)
return
MAXX(_t2,[Value])

(5)Then we can put the measure on the visual and we can meet your need:

Thank you for your time and sharing, and thank you for your support and understanding of PowerBI! 

Best Regards,

Aniya Zhang

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