Subtract todays total from previous day total if current month

[gpl]

Hey yall, thanks for all the help you guys provide! Hopefully someone can tell me how to do this as I have been struggling to figure this one out. I have a table that increments sales for the month and I am trying to get daily by subracting from previous day. I also don't want it to subtract if previous day is in a different month.

What I have:

Date          Sales

8/28/2021 91000

8/29/2021 91500

8/30/2021 91700

8/21/2021 92200

9/1/2021   450

What I want:

What I Have

Date          Sales     Daily Sales

8/28/2021 91000   

8/29/2021 91500   500

8/30/2021 91700   200

8/21/2021 92200   500

9/1/2021   450       450

Hopefully someone can help and I appreciate all the great resources here!

[smpa01 · Accepted solution]

@gpl  Can you try the following which sums on the subtotal level as well

dailySales = 
SUMX (
    'fact',
    VAR _prevDate =
        MAXX (
            FILTER ( ALL ( 'fact'[Date] ), 'fact'[Date] < EARLIER ( 'fact'[Date] ) ),
            'fact'[Date]
        )
    VAR _prevMonth =
        MONTH ( _prevDate )
    VAR _currentDate =
        CALCULATE ( MAX ( 'fact'[Date] ) )
    VAR _currentMonth =
        MONTH ( _currentDate )
    VAR _prevDateSale =
        MAXX ( FILTER ( ALL ( 'fact' ), 'fact'[Date] = _prevDate ), 'fact'[Sales] )
    VAR _currentDateSale =
        CALCULATE ( SUM ( 'fact'[Sales] ) )
    VAR _diff =
        SWITCH (
            TRUE (),
            _prevMonth = BLANK (), BLANK (),
            _currentMonth = _prevMonth, _prevDateSale - _currentDateSale,
            _currentDateSale
        )
    RETURN
        IF ( _diff < 0, ABS ( _diff ), _diff + 0 )
)

[gpl]

Your a genius; is it possible if I put that measure in a table to get it to sum just those values? It is summing for TotalSales. Ideally the table to the right would show $14249

[DataInsights]

@gpl,

Try these measures:

Total Sales = SUM ( Table1[Sales] )

Daily Sales = 
VAR vDate =
    MAX ( Table1[Date] )
VAR vMinDate =
    CALCULATE ( MIN ( Table1[Date] ), ALLSELECTED ( Table1[Date] ) )
VAR vCurrentMonth =
    MONTH ( vDate )
VAR vCurrentAmount = [Total Sales]
VAR vPrevAmount =
    CALCULATE (
        [Total Sales],
        Table1[Date] = vDate - 1,
        MONTH ( Table1[Date] ) = vCurrentMonth
    )
VAR vResult =
    SWITCH (
        TRUE (),
        vDate = vMinDate, BLANK (),
        ISBLANK ( vPrevAmount ), vCurrentAmount,
        vCurrentAmount - vPrevAmount
    )
RETURN
    vResult

I assumed the 8/21/2021 date should be 8/31/2021.