MDX YTD Calculated Member for current and parallel period - mdx

Question

Trying to build a calculated member using our date hierarchy for use in Tableau.
Hierarchy is as follows:
Fiscal Year
Fiscal Season
Fiscal Quarter
Fiscal Month
Fiscal Week
Date
To help our users with their analysis on dashboards, we're looking to build a Tableau set including the following members for them to toggle through:
Yesterday, Week to Date, Month to Date, Season to Date, and Year to Date.
We need to be able to show Sales $ and Sales $ LY(measure is defined as parallel period) together and be able to toggle through the different "to date" values. The this year portion is fine, but creating a calculated member that works appropriately for the LY measure too has been problematic. We need to be able to pivot between the periods for dashboards rather than create individual measures for each period TY and LY.
Here are the current definitions we have out there:
Yesterday: [DATE].[Time].defaultmember
WTD: [DATE].[Time].defaultmember.parent
MTD: [DATE].[Time].defaultmember.parent.parent
STD: [DATE].[Time].defaultmember.parent.parent.parent
YTD: [DATE].[Time].defaultmember.parent.parent.parent.parent
Any thoughts on how to modify these so that the LY measure reflects the same "to date" period rather than the full period last year?

Answer 1

Count the number of days completed this year and then use the Head function to get the same set of dates from the previous year - aggregate that set together.
Here is an illustration against the AdvWrks cube:
WITH
SET [DaysThisYear] AS
Descendants
(
[Date].[Calendar].[Calendar Year].&[2007]
,[Date].[Calendar].[Date]
)
MEMBER [Measures].[posOfCurrentDate] AS
Rank
(
[Date].[Calendar].CurrentMember
,Descendants
(
[Date].[Calendar].Parent.Parent.Parent.Parent
,[Date].[Calendar].[Date]
)
)
MEMBER [Measures].[prevEquivMTD] AS
Sum
(
Head
(
Descendants
(
[Date].[Calendar].Parent.Parent.Parent.Parent.PrevMember
,[Date].[Calendar].[Date]
)
,[Measures].[posOfCurrentDate]
)
,[Measures].[Internet Sales Amount]
)
MEMBER [Measures].[posCurrentYear] AS
[Date].[Calendar].Parent.Parent.Parent.Parent.Member_Caption
SELECT
{
[Measures].[posCurrentYear]
,[Measures].[posOfCurrentDate]
,[Measures].[Internet Sales Amount]
,[Measures].[prevEquivMTD]
} ON 0
,
[Date].[Calendar].[Date].&[20050111]
:
[Date].[Calendar].[Date].&[20080611] ON 1
FROM [Adventure Works];
This is the above as a single measure:
WITH
MEMBER [Measures].[Internet Sales Amount prevEquivMTD] AS
Sum
(
Head
(
Descendants
(
[Date].[Calendar].Parent.Parent.Parent.Parent.PrevMember //previous year
,[Date].[Calendar].[Date]
)
,Rank
(
[Date].[Calendar].CurrentMember
,Descendants
(
[Date].[Calendar].Parent.Parent.Parent.Parent //current year
,[Date].[Calendar].[Date]
)
)
)
,[Measures].[Internet Sales Amount]
)
SELECT
{
[Measures].[Internet Sales Amount]
,[Measures].[Internet Sales Amount prevEquivMTD]
} ON 0
,
[Date].[Calendar].[Date].&[20050111]
:
[Date].[Calendar].[Date].&[20080611] ON 1
FROM [Adventure Works];
Unfortunately it is tied to the measure Internet Sales Amount so not very generic. Generic calcs such as prev equiv mtd or Year on Year growth are usually added to a helper Time Caculation helper dimension that is independent from the Date dimension.