MDX custom consolidation: consolidate only last level descendants - ssas

Question

I'm looking for a elegant MDX expression that sum values only of the elements of last level dimension:
I have a measure M , also I have a hierarchical parent - child dimension U that is non balanced tree:
R -> ( M = R1 + R2 = 157 )
..R1 -> ( M = R11 + R12 = 150 )
...R11 -> ( M=R111 = 100 )
.....R111 -> M=100
...R12 -> M = 50
..R2 -> M = 7
I have a set that contains some elements from this dimension:
S contains R11, R111, R12
Now I need to take, for a U.currentMember the M value (that is, the sum of last level descendants)
I have written this expression, it works but perhaps they are a more elegant way to write it:
with member measures.XX as
sum (
intersect(
[S],
Except(
descendants( [U].currentMember ),
existing( descendants( [U].currentMember ).item(0) )
)
)
,
[M]
)
select
measures.xx on columns
from [CUBE]
where [U].[R]
Note: This MDX dont run:
with member measures.XX as
sum (
intersect(
[S],
descendants( [U].currentMember )
)
,
[M]
)
select
measures.xx on columns
from [CUBE]
where [U].[R]
because return 250 insteat 150.
Right result is 150: R11 + R12 (because R111 is included in R11).
Bad result is: 250: '100' value is taked for twice R11 + R111.
Final Solution:
with member measures.XX as
sum(
intersect (
descendants([U].currentMember,,leaves),
[S]
)
,
[M]
)
select
measures.XX on 0,
descendants( [Unitats].[Unitat].[All] ) on 1
from [C]

Answer 1

Not sure what you want to calculate but let's assume [Member] is the member you want to evaluate :
I'd use the descendants, filter and isLeaf MDX functions :
Sum(
Filter( Descendants( [Member] ), isLeaf(Member_hierarchy.currentmember) )
,[M])
You're adding all descendants including itself that are leafs (no children).