What's the difference between two dax calculations for Date Difference?

[sonisick]

What's the difference between two dax calculations for Date Difference?

Duration = Format(LASTDATE(FactInternetSales[DueDate])- FIRSTDATE(FactInternetSales[DueDate]),"0") +1

Difference Last Minus First = ABS(DATEDIFF(LASTDATE(FactInternetSales[DueDate]), FIRSTDATE(FactInternetSales[DueDate]), day))+1

If I use the first one on a Matrix display, I can't descend the Hierarchy. I get an error:

Couldn't load the data for this visual: MdxScript(Model) (11,38) Calculation error in measure 'FactInternetSales[Duration]: Cannot convert value '' of type Text to Number.

The Second works fine.

[Daryl-Lynch-Bzy · Accepted solution]

Hi @sonisick - this is make sense because FIRSTDATE - DAX Guide and LASTDATE - DAX Guide are table functions.  This means the function produce results in a Table.  So you are effectively asking for Table A - Table B.  I guess the FORMAT allows the results to be converted to Text String that looks like a number.  When using the DATEDIFF - DAX Guide function instead of minus, the result is a Scalar value.  This mean the function produces a single integer value.

Try the following instead as MAX and MIN are scalar functions.

Duration Max/Min = MAX(FactInternetSales[DueDate])- MIN(FactInternetSales[DueDate]) + 1

[Seanan]

Hi @sonisick 

At first glance it is because in your first expression you have 0 wrapped in quotations. By doing this Power BI will then format the expression as text. Could you try removing the quotations to see if this changes anything.

[sonisick]

Thanks for your answer, but unquoting doesn't help the problem.

[Daryl-Lynch-Bzy]

Hi @sonisick - The FORMAT – DAX Guide function will convert the Number result to Text string.   The ABS value will retain the number value.  This is why the visual is becoming confused when you try sorting the heirarchy.

[sonisick]

This is the expression the instructor started from

DurationWOFormat = LASTDATE(FactInternetSales[DueDate])- FIRSTDATE(FactInternetSales[DueDate])

Which gives something totally incomprehensible to me.

Year,Quarter,Month,Day,Earliest DueDate,Latest DueDate,YearStart,DurationWOFormat
2011,Qtr 1,January,10,2011-01-10 00:00:00,2011-01-10 00:00:00,2011-01-10 00:00:00,1899-12-30 00:00:00
2011,Qtr 1,January,11,2011-01-11 00:00:00,2011-01-11 00:00:00,2011-01-10 00:00:00,1899-12-30 00:00:00
2011,Qtr 1,January,12,2011-01-12 00:00:00,2011-01-12 00:00:00,2011-01-10 00:00:00,1899-12-30 00:00:00
2011,Qtr 1,January,13,2011-01-13 00:00:00,2011-01-13 00:00:00,2011-01-10 00:00:00,1899-12-30 00:00:00