Converting single result of an MDX set query to a calculated measure - set

Question

I have a SET calculated member that returns me the first invoice date of a specific client ID. This set uses the CurrentSalesPeriod which is also a single result generated from a set.
The problem is that I want to find a workaround so that I'm not forced to use this set on my rows. I would like to make this a measure so I can use it in my columns and for other purposes.
Could anyone help me with that? Is it possible at all in MDX? The query below is working but I would like to use this in another query where I am not allowed to put it on the rows.
SET [First Invoice Date] AS
Iif(
COUNT(
NonEmpty(
[Date invoice].[Invoice date].[Invoice date],
[CurrentSalesPeriod]
* Ytd(StrToMember(#PAR_Date).Parent.Lag(1).LastChild)
* [Point of sale].[Client id].&[46]
* {[Measures].[YTD Sales]}
)
) = 0,
{[Date invoice].[Bonus Calendar - Week].[All].UNKNOWNMEMBER.UNKNOWNMEMBER},
Head(
NonEmpty(
[Date invoice].[Invoice date].[Invoice date],
[CurrentSalesPeriod]
* Ytd(StrToMember(#PAR_Date).Parent.Lag(1).LastChild)
* [Point of sale].[Client id].&[46]
* {[Measures].[YTD Sales]}
), 1
)
)
SET [CurrentSalesPeriod] AS
Tail(
NonEmpty(
[Point of sale].[Management period].[Management period],
{[Measures].[Sales amount]}
* Ytd(StrToMember(#PAR_Date))
* [Point of sale].[Client id].&[46]
), 1
)

Answer 1

Pick a dimension that is not going to be used, and tag on an aggregated member that is the aggregation of your custom set - I don't know your cube but try replacing [AnotherDimension].[AnotherHierarchy]. in the following with a little used Dim.Hier in your cube:
SET [First Invoice Date] AS
Iif(
COUNT(
NonEmpty(
[Date invoice].[Invoice date].[Invoice date],
[CurrentSalesPeriod]
* Ytd(StrToMember(#PAR_Date).Parent.Lag(1).LastChild)
* [Point of sale].[Client id].&[46]
* {[Measures].[YTD Sales]}
)
) = 0,
{[Date invoice].[Bonus Calendar - Week].[All].UNKNOWNMEMBER.UNKNOWNMEMBER},
Head(
NonEmpty(
[Date invoice].[Invoice date].[Invoice date],
[CurrentSalesPeriod]
* Ytd(StrToMember(#PAR_Date).Parent.Lag(1).LastChild)
* [Point of sale].[Client id].&[46]
* {[Measures].[YTD Sales]}
), 1
)
)
SET [CurrentSalesPeriod] AS
Tail(
NonEmpty(
[Point of sale].[Management period].[Management period],
{[Measures].[Sales amount]}
* Ytd(StrToMember(#PAR_Date))
* [Point of sale].[Client id].&[46]
), 1
)
MEMBER [AnotherDimension].[AnotherHierarchy].[Agg_FirstInvoiceDate] AS
Aggregate(
[First Invoice Date]
)
...
...

Answer 2

I am not sure why you want this set as a measure and what it's implication might be, but if you want the date as a measure, then you can simply add one more calculated measure and use the membervalue property to store the value of this date. Adding the definition of the calculated measure only..
MEMBER Measures.FirstInvoiceDate AS
[First Invoice Date].Item(0).MEMBERVALUE
In the final select, just use this new measure. Let me know how it works for you.