Ranking in MDX (handling negative numbers)

Question

Hi,
I have a measure in my SSAS 2008  cube that returns the rank of a product based on its growth %. The MDX definition is below:
IIF(ISEMPTY([Measures].[Growth %]), NULL,
RANK([Dim Products].[Parent Products].CURRENTMEMBER, [Dim Products].[Parent Products].[Parent Products].MEMBERS, [Measures].[Growth %]))
This works fine when the growth % is positive. But when the % is negative, it returns weird results. Example:
  Growth %  |  Rank
     290 %          1
     9.71 %         5
    12.19 %        4
    -78.52%      269
   - 18.35%      267
There are only 9 products in this dimension.
Does anyone have any idea how I can tweak the MDX so that it returns a proper rank even when the growth % is negative?
Thank you in advance for your help!

Answer 1

The is no problem with ranking. This SSAS 2008 example proves it:
WITH MEMBER Measures.MarginRank AS
iif( IsEmpty( [Measures].[Reseller Gross Profit Margin] ), null,
Rank( [Product].[Color].CurrentMember,
-- NonEmpty(
[Product].[Color].[Color].MEMBERS,
-- [Measures].[Reseller Gross Profit Margin]),
[Measures].[Reseller Gross Profit Margin] )
SELECT
[Measures].[Reseller Gross Profit Margin], Measures.MarginRank } on 0,
Order( [Product].[Color].[Color].MEMBERS, [Measures].[Reseller Gross Profit Margin], BDESC ) on 1
FROM
[Adventure Works]
Results look like this:
Reseller Gross Profit Margin MarginRank
White 36,39% 1
NA 29,28% 2
Silver/Black 25,94% 3
Silver 6,23% 4
Black 4,17% 5
Grey (null) (null)
Multi -2,09% 7
Red -2,22% 8
Blue -3,87% 9
Yellow -9,46% 10
Now, what you need to do in order to skip blanks is apply NonEmpty() over set on rows. See 2 lines I commented and remove comments. That will give you only 9 ranks; last 4 will be shifted down by one place. I deliberately made queries withouth NON EMPTY, to show you the behavior.
Reseller Gross Profit Margin MarginRank
White 36,39% 1
NA 29,28% 2
Silver/Black 25,94% 3
Silver 6,23% 4
Black 4,17% 5
Grey (null) (null)
Multi -2,09% 6
Red -2,22% 7
Blue -3,87% 8
Yellow -9,46% 9
Why did it happen to you since you only have 9 products as you claim?
I assume you have a parent-child dimension (because of the behavior and because the name suggests so). It was my first guess, but I wanted to make a nice example and a case using Adventure Works, so that everyone can test.
You must be considering the first level only, where there are only 9 products in your hierarchy. Well, in P/C item ordinals don't run per level. They run per branches and don't reset ever (no matter the level). So, the second member in the first level might have rank i.e. 13 if there are 11 descendants under the first member in level one of P/C. 1+11below = 12 so far, so the next one is 13.
Try the same example using Employee dimension. And you'll see ranks above 200.
Again, the same solution works, so apply NonEmpty()!
Regards,
Tomislav Piasevoli
Business Intelligence Specialist
www.softpro.hr