SSRS 2008 Matrix - Column Data Incorrect

Question

I am trying to convert an old local Crystal Report. Basically, for a given order, there are multiple line items. The report needs to show Order and Vendor in the left two columns, then a variable number of columns (that fit on a page) to display the line numbers.

To do this, I added a Matrix, and adding the groupings and all that. However, I get only one line item for each Order/Vendor combination, even though each combination has at least two line items.

Current:

============================================
+ Order     + Vendor      + Item 1 + Item 2 ...
============================================
+ OrdValue1 + VendValue1  + Value  + [blank]
============================================
+ OrdValue2 + VendValue2  + [blank]+ Value
============================================

Desired:

============================================
+ Order     + Vendor      + Item 1 + Item 2 ...
============================================
+ OrdValue1 + VendValue1  + Value  + Value
============================================
+ OrdValue2 + VendValue2  + Value  + Value
============================================

Edit:

Answer 1

I would go back to the source Dataset (assuming it is SQL) and add a Column_Number calculation which resets to 1 for each Order + Vendor combination, e.g.

ROW_NUMBER () OVER ( PARTITION BY Order , Vendor ORDER BY Line_Number ) AS Column_Number

Then I would edit the Column Group defintion to use that Column_Number column.