Using the MDX lag and lead functions - ssas

Question

I'm attempting to query an SSAS cube using MDX, I have a list of numeric values which are ordered in the cube and I want to refer to an adjacent cell in the cube in order to return the value.
WITH MEMBER Measures.[LastShift]<br>
AS<br>
(<br>
[Measures].[Impact Value GBP], <br>
[Dim Shift].[Shift Value1].PrevMember<br>
)<br>
MEMBER Measures.[NextShift]<br>
AS<br>
(<br>
[Measures].[Impact Value GBP], <br>
[Dim Shift].[Shift Value1].NextMember<br>
)<br>
SELECT <br>
{NONEMPTY([Measures].[Impact Value GBP]), <br>
Measures.LastShift,<br>
Measures.NextShift<br>
}<br>
ON 0,<br>
NONEMPTY([Dim Shift].[Shift Value1].[Shift Value1])<br>
ON 1<br>
FROM [factTradeValues]<br>
I can see in the RDBMS that I do have adjacent values, but I cannot get the MDX to return anything other than null. Maybe I'm being thick, but cannot see the solution.
Thanks for any help

Answer 1

PrevMember and NextMember are "member functions" so you need do something like this...
WITH
MEMBER Measures.[LastShift] AS
(
[Dim Shift].[Shift Value1].CurrentMember.PrevMember,
[Measures].[Impact Value GBP]
)
MEMBER Measures.[NextShift] AS
(
[Dim Shift].[Shift Value1].CurrentMember.NextMember,
[Measures].[Impact Value GBP]
)

Answer 2

To answer my own question there turned out to be issues with prevmember and nextmember, because I wanted to refer to the next item in turns of the context of my criteria. I actually wanted to refer to the next item in my set, which is subtly different.
In order to refer to an item in a set you use item and then I used rank to get the adjacent cell.
/* Define the shifts appropriate for this scenario */
SET [SpotShifts] AS
EXCEPT(
NONEMPTY([Dim Shift].[Shift Value1].[Shift Value1].MEMBERS,
(
[Dim Shift Entity].[Shift Entity].[GBP/FTSE],
[Dim Date].[Date].[Date].&[20120305],
{PriceImpacts
}
,[Dim Instrument].[Arena Name].[CO/GBP/Lch10/FTSE/140908/Inc_Quarter/5L]
)),[Dim Shift].[Shift Value1].&[0])
MEMBER Measures.CurrentSpotShift
AS
StrToValue([Dim Shift].[Shift Value1].CURRENTMEMBER.NAME)
MEMBER Measures.NextSpotShift AS
IIF((Measures.CurrentSpotShift<0),
SpotShifts.Item(RANK([Dim Shift].[Shift Value1].CURRENTMEMBER,SpotShifts)-2).NAME,
SpotShifts.Item(RANK([Dim Shift].[Shift Value1].CURRENTMEMBER,SpotShifts)).NAME)
MEMBER Measures.PreviousSpotShift AS
IIF((Measures.CurrentSpotShift<0),
SpotShifts.Item(RANK([Dim Shift].[Shift Value1].CURRENTMEMBER,SpotShifts)).NAME,
SpotShifts.Item(RANK([Dim Shift].[Shift Value1].CURRENTMEMBER,SpotShifts)-2).NAME)
MEMBER Measures.NextValue AS
IIF(Measures.CurrentSpotShift>0,
([Measures].[Impact Value],SpotShifts.Item(RANK([Dim Shift].[Shift Value1].CURRENTMEMBER,SpotShifts))),
([Measures].[Impact Value],SpotShifts.Item(RANK([Dim Shift].[Shift Value1].CURRENTMEMBER,SpotShifts)-2))
SELECT { NONEMPTY([Measures].[Impact Value]),
(Measures.PreviousSpotShift),
(Measures.LastValue),
(Measures.NextSpotShift),
(Measures.NextValue)} ON 0,
NONEMPTY(SpotShifts) ON 1
FROM factTradeCube
I hope this helps somebody as I found the use of rank within item as not an obvious solution to this, but the only one that got me the correct results.