current vs previous week count

[tatenda24]

Hi Everyone, 
i have seen that dax doesnt have a previous week function, can someone assist in writing a measure that shows previous week counts to compare to that current week count as shown in the tables below. 

The first table is a representation of the actual data and the second table is the desired outcome.

If anyone can assist in writing such a measure I would greatly apreciate it,

Thank you 

Data table 

Expected outcome 

[amitchandak]

@tatenda24 , Please check the solution by @vapid128 , The solution work well within a year. Across year week need week rank column. Prefer a date table

new columns

Week Rank = RANKX(all('Date'),'Date'[Week Start date],,ASC,Dense)
OR
Week Rank = RANKX(all('Date'),'Date'[Year Week],,ASC,Dense) //YYYYWW format

New measure examples
This Week = CALCULATE(sum('Table'[Qty]), FILTER(ALL('Date'),'Date'[Week Rank]=max('Date'[Week Rank])))
Last Week = CALCULATE(sum('Table'[Qty]), FILTER(ALL('Date'),'Date'[Week Rank]=max('Date'[Week Rank])-1))

Power BI — Week on Week and WTD
https://medium.com/@amitchandak.1978/power-bi-wtd-questions-time-intelligence-4-5-98c30fab69d3
https://community.powerbi.com/t5/Community-Blog/Week-Is-Not-So-Weak-WTD-Last-WTD-and-This-Week-vs-La...
https://www.youtube.com/watch?v=pnAesWxYgJ8

[vapid128 · Accepted solution]

Var _maxWeekNum = max(weeknum)

return

Calculate(

    countrows(table),

    filter(

        all(table),

        table[weeknum] = _maxWeekNum - 1

    )

)