How to calculate difference of values for rows of the same column?

[talitanieps]

Hello PBI Community! Hope you are doing all right! 🙂

I need some assistance to calculate the difference between values of a same column; this is for a social media database, and the measure I had working just fine it's simply not anymore.

The data is appended everyday for different accounts, which here are represented by A, B and C, and the dates are from the column date.

The problem is that I need to calculate and show the amount of new followers acquired between two dates (usually a full month, but it needs to be flexible), and the data is not always organized by date and/or product:

For example, I'd need to calculate the difference  between may 17th and 18th for name A, that is 
88961-88889, but the values are separated by other values:

date	name	total_followers
18/05/2023	A	88961
18/05/2023	B	2882
18/05/2023	C	1935
17/05/2023	A	88889
17/05/2023	B	2868
17/05/2023	C	1935
16/05/2023	A	88793
16/05/2023	B	2858
16/05/2023	C	1937
15/05/2023	A	88710
15/05/2023	B	2848
15/05/2023	C	1936
14/05/2023	A	88674
14/05/2023	B	2847
14/05/2023	C	1937
13/05/2023	A	88674
13/05/2023	B	2847
13/05/2023	C	1937
12/05/2023	A	88580
12/05/2023	B	2832
12/05/2023	C	1935
11/05/2023	A	88514
11/05/2023	B	2794
11/05/2023	C	1929
10/05/2023	A	88459
10/05/2023	B	2784
10/05/2023	C	1924
09/05/2023	A	88373
09/05/2023	B	2766

Also, I'm currently using this Dax Formula to do the math, but it's not working (showing 0):

this firstdate() and lastdate() are supposed to get the dates from a date slicer, using a calendar table:

Measure = 

VAR _FollowersOnLastDate =
CALCULATE(
    MAX( Table[total_followers] ) ,
    FILTER( Table ,
            AND( Table[name] = SELECTEDVALUE( 'Table _ Media'[produto] ) ,
                  DATEADD ( FILTER ( DATESMTD ( d_Calendar[Date]), d_Calendar[Date] < TODAY()), -1, MONTH)) +0
            )
    )
)

VAR _FollowersOnFirstDate =
CALCULATE(
    MAX( Table[total_followers] ) ,
    FILTER( Table ,
            AND( Table[name] = SELECTEDVALUE( 'Table _ Media'[produto] ) ,
                  DATEADD ( FILTER ( DATESMTD ( d_Calendar[Date]), d_Calendar[Date] < TODAY()), -1, MONTH)) +0
            )
    )
)

VAR _MinFollowers =
CALCULATE(
    MIN( Table[total_followers] ) ,
    FILTER( Table ,
            Table[name] = SELECTEDVALUE( 'Table _ Media'[produto] )
    )
)

-------------------------------------------------------
RETURN _FollowersOnLastDate - _FollowersOnFirstDate

 SWITCH(
     TRUE() ,
     LASTDATE( d_Calendar[Date] ) <= MIN( Table[date] ) , 0 ,
     FIRSTDATE( d_Calendar[Date] ) < MIN( Table[date] ) , _FollowersOnLastDate - _MinFollowers ,
     _FollowersOnLastDate - _FollowersOnFirstDate
     ) +0

Any suggestions on how to improve this code, or to do the calculation as per I explained above?

Thanks once again for the assistance, in advance! 🙂

Best Regards,

[Greg_Deckler]

@talitanieps See my article on Mean Time Between Failure (MTBF) which uses EARLIER: http://community.powerbi.com/t5/Community-Blog/Mean-Time-Between-Failure-MTBF-and-Power-BI/ba-p/3395....
The basic pattern is:
Column = 
  VAR __Current = [Value]
  VAR __PreviousDate = MAXX(FILTER('Table','Table'[Date] < EARLIER('Table'[Date])),[Date])

  VAR __Previous = MAXX(FILTER('Table',[Date]=__PreviousDate),[Value])
RETURN
  __Current - __Previous

[talitanieps]

Hello @Greg_Deckler , 

Thanks a lot for your reply!
I'll review that and let you know of the results, thanks again! 🙂

Best regards, 

Talita.