You would probably need to show examples of what you have in mind there:
- Numeric columns in which values are combined arithmetically in some way ?
- Text columns in which values are concatenated together ?
- as single lines ?
- Something quite different ?
One way or another, it sounds like something which would need a custom script or plugin.
See also:
How to Merge Two Columns? - OmniOutliner / OmniOutliner for Mac - The Omni Group User Forums
