Ah, ok, I think I see what you are referring to now.

One way to do this would be to use a Dictionary object. The dictionary would be defined as:

Code:
Dictionary<string, DataObjects.UserGroupDetails>
where the first type (string) would be your User ID. When you are looping through your other dataset, and you find a User Id that you want to "look up" you can index into the Dictionary using the User Id and return the DataObjects.UserGroupDetails directly.

Hope that makes sense!

Gary