how to get a year history of data in dax - excel

Question

IIF(SUM
(
[Calendar].[Month].CurrentMember.Lag(11) :
[Calendar].[Month].CurrentMember,
[Measures].[Qty]
) = 0, 0,
SUM
(
[Calendar].[Month].CurrentMember.Lag(11) :
[Calendar].[Month].CurrentMember,
[Measures].[Num]
) /
SUM
(
[Calendar].[Month].CurrentMember.Lag(11) :
[Calendar].[Month].CurrentMember,
[Measures].[Qty]
) )
This is formula from multi dimensional model i am trying to convert this MDX formula to DAX formula to use in Tubular model.
12 Month Avg :=
IF (
CALCULATE (
SUM ( [QTY] ),
FILTER (
ALL ( Calendar[Month] ),
Calendar[Month] - 11
= ( Calendar[Month] - 11 )
)
)
= 0,
BLANK (),
CALCULATE (
SUM ( [Num] ),
FILTER (
ALL ( Calendar[Month] ),
Calendar[Month] - 11
= ( Calendar[Month] - 11 )
)
)
/ CALCULATE (
SUM ( [QTY] ),
FILTER (
ALL ( Calendar[Month] ),
Calendar[Month] - 11
= ( Calendar[Month] - 11 )
)
)
)
So i made this DAX formula to convert MDX formula at the top. However it seem not working properly when i select month in pivot table. Those two formula don't match when i filtered by month. How can i resolve that problem?

Answer 1

1) Create three base measures:
TotalNum := SUM([Num])
TotalQty := SUM([Qty])
Avg := DIVIDE ( [TotalNum], [TotalQty], 0 )
2) Create a calculated measure to calculate the average over the prior year including the current selected month:
AvgLastYear:= CALCULATE (
[Avg] ,
DATESINPERIOD (
Calendar[Date] ,
MAX(Calendar[Date]),
-1, year
)
)
Explanation:
First, you don't need that divide by zero rigmarole, both MDX and DAX have a DIVIDE() function which handles that implicitly.
Second, with DAX, the idea is to build a base measure and then use CALCULATE() to shift the context of that measure as needed - in this case the time period.
Here we're looking at the current selected month (represented as MAX(Calendar[Date]), though you could use any aggregation function) and then using DATESINPERIOD() to choose a set of dates in our Calendar table which represent the time period T-1 year to the current month.