Calculate Time Interval in SSAS based on difference between current row time and previous row time - ssas

Question

I have an SSAS Cube which tracks the movement of items in a warehouse. Items are scanned into various locations, so, we have a date and time (HH:MM:SS) that the item is scanned. We want to be able to create a calculated measure, which is not pre-defined on the fact table, as we would like it to be dynamic, based on the attributes the query is sliced by.
So, in order to accommodate that, I figured I would create a SET which has the intersection of valid dates and valid times, like this:
WITH SET [Valid Date]
AS FILTER([WMSR Date].[Full Date].[Full Date].MEMBERS,[Measures].[Fact Scans Count]>0)
SET [Valid Time]
AS FILTER(([Valid Date]*[Time].[Full Time].[Full Time].MEMBERS),[Measures].[Fact Scans Count]>0)
So, if I run this:
SELECT {[Measures].[Fact Scans Count]} ON COLUMNS,
[Valid Time] ON ROWS
FROM
WarehouseCube
WHERE
[Piece].[Dim ID Key].&[1127981]
It will give me, for a given item, the date/time of the scan, and the count. How do I get the date/time from the previous row?
Thanks in advance!

Answer 1

You could use
[ValidTime].Item(Rank(([WMSR Date].[Full Date].CurrentMember, [Time].[Full Time].CurrentMember),
[ValidTime])
- 2
)
The Rank function returns the position of a tuple within a set. The Item function returns a tuple at a position from a set.
As Rank returns 1 for the first item, while Item expects 0 for the first item, and you want to go back one position, you need to subtract two.