Calculating difference between rows by date

[trotsale]

Hello!

I have a problem and here it is:

In my Power Bi I have a table with report which is getting data from local folder. A key is date, which is adding as a column on every refresh. It looks like this: 

 I already have a measure which counts number of devices by date, it seems like

DevicesByDate = CALCULATE(COUNTROWS('Table');DISTINCT('Table'[Date]))

But I can`t get a measure which will substract number of DevicesByDate from previous date (Example: 4 devices by 08/15/2017-4 devices by 07/21/2017 = 0). 

Can you please help me guys?

Thanks!

[GilbertQ]

Off the top of my head have you tried another calculation which would use the PREVIOUSDAY DAX function?

Devices Previous Day = CALCULATE([Devices],PREVIOUSDAY('Date Table'[Date]))

You would need to have a Date table in order for this to work. I think it might look for the Previous Day being 08/14/2017 though.

[Anonymous · Accepted solution]

Hi @trotsale

Try out this method. This method grabs the device ids from last month and subtracts them from device ids this month.

DevicesByDate difference last month compared to this month = CALCULATE(COUNTROWS('Test');DISTINCT('Test'[Date]);DATEADD(DATESBETWEEN(Test[Date];STARTOFMONTH(Test[Date]);ENDOFMONTH(Test[Date]));-1;MONTH)) - CALCULATE(COUNTROWS('Test');DISTINCT('Test'[Date]);DATESINPERIOD(Test[Date];LASTDATE(Test[Date]);-1;MONTH)) 

Best,

Martin

[Anonymous]

@trotsale Did it work out for you?

[trotsale]

Thank you so much for help! 

It works now, but it displays uptake only when graphic is shown by quarter or year. When I choose display by month, It shows me number of devices. Maybe I should change dates period?By year

By month

[trotsale]

I`ve tried this and here is what i got:

 Here is the way I used DAX: 

 My DateTable consists of 2 dates (07/21/2017 and 08/14/2017). Am I doing something wrong?