Day over Day Dax question

[Anonymous]

I have a data set that has a list of 5 different products and daily prices for each, for example

Date    Product    Price

09/09     A            $1.00

09/09     B             $1.50

09/09     C             $0.50

09/08     A             $0.75

09/08     B             $1.25

09/08     C             $1.30

I also have a date table set up for this BI report. I need to calculate day over day change and need some help figuring out the DAX. Prices are only published Mon-Friday, so I need the DAX to recognize not to calculate if there isn't a price for the previous date (Ex, weekends and holidays). Maybe the Dax can just take most recent price and the last price and get the difference?

Thank you for your help. 

[amitchandak]

@Anonymous , Try a new column like

new column =
var _max = MAXX(FILTER(Table,[Date] < EARLIER([Date]) && [Product] = EARLIER([Product])),[Date])
return
[Price]- MAXX(FILTER(Table,[Date] =_date && [Product] = EARLIER([Product])),[Price])

[Greg_Deckler]

@Anonymous You need to EARLIER. 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/339586.
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

[Anonymous]

This got me close but not exact. Below is a list of the numbers I need vs what the DAX formau you provided is giving me. I think I need to add a filter for product somewhere, but I just can't get it right. I checked on excel using basic formaul of (current-previous)/previous). On my report, I will end up showing these numbers as %Change Day over Day

Date          Product      Price        Day over Day change      # retruned from DAX formual

09/01            A             1.4650

09/02            A             1.5100             0.0307                           -0.49670

09/03            A             1.5000             -0.0066                         -0.50000

09/04           A              1.4925            -0.0050                           -0.50250

09/01           B              1.8025

09/02           B              1.9100               0.0596                          -0.36330

09/03           B              2.0525               0.0746                         -0.31580

09/04           B              2.1250               0.0353                           -0.29170

[Anonymous]

This got me close but not exact. Below is a list of the numbers I need vs what the DAX formau you provided is giving me. I think I need to add a filter for product somewhere, but I just can't get it right. I checked on excel using basic formaul of (current-previous)/previous). On my report, I will end up showing these numbers as %Change Day over Day

Date          Product      Price        Day over Day change      # retruned from DAX formual

09/01            A             1.4650

09/02            A             1.5100             0.0307                           -0.49670

09/03            A             1.5000             -0.0066                         -0.50000

09/04           A              1.4925            -0.0050                           -0.50250

09/01           B              1.8025

09/02           B              1.9100               0.0596                          -0.36330

09/03           B              2.0525               0.0746                         -0.31580

09/04           B              2.1250               0.0353                           -0.29170