Adjust TOPCOUNT to be time aware - mdx

Question

Got the following script but it seems to pull back the top 15 customers by NumDeals that they have made over all time - rather than by the last 7 days.
How do I adjust the set to reflect this requirement?
WITH
SET [Set_7Days] as
TAIL ([Date].[Date - Calendar Month].[Calendar Day], 7)
SET [Set_Top15Customers] as
{
TOPCOUNT (
[CustomerDim].[CustomerDim].[CustomerLevel].members,
15,
(
[Date].[Date - Calendar Month].currentmember,
[Measures].[NumDeals]
)
)
}
SELECT
NON EMPTY
[Set_7Days]
ON COLUMNS,
NON EMPTY
[Set_Top15Customers]
ON ROWS
FROM [ourCube]
WHERE (
[Measures].[NumDeals]
)
EDIT
Using mmarie help I've got the following: wanted to keep things in a custom set so that I can add it to a PIVOT connected to a CUBE in EXCEL:
WITH
SET as
TAIL ([Date].[Date - Calendar Month].[Calendar Day], 7)
SET [Set_Top15Customers] as
{
TOPCOUNT (
[CustomerDim].[CustomerDim].[CustomerLevel].members,
15,
Sum(
[Set_7Days], //TAIL([Date].[Date - Calendar Month].[Calendar Day], 7),
[Measures].[NumDeals]
)
)
}
SELECT
NON EMPTY
[Set_7Days]
ON COLUMNS,
NON EMPTY
[Set_Top15Customers]
ON ROWS
FROM [ourCube]
WHERE (
[Measures].[NumDeals]
)

Answer 1

You need to add the date filter into your top count. There are probably a few ways to do this. This one works, but you might have to check performance to see if it is acceptable.
Try this:
with
member [measures].[Num Deals last 7 days] as
Sum(Head([Date].[Date - Calendar Month].[Calendar Day], 7), [Measures].[NumDeals])
select
NON Empty {TAIL ([Date].[Date - Calendar Month].[Calendar Day], 7)[measures].[Num Deals Last 7 days]} on 0,
NON Empty {topcount( {[CustomerDim].[CustomerDim].[CustomerLevel].members}, 5, measures.[Num Deals last 7 days])} on 1
FROM [ourCube]
WHERE ( [Measures].[NumDeals] )