How to display only one row?

[eluser]kr1pt[/eluser]
Hi all, I have xy rows (private messages system) in the database, and I have from_id = 2, to_id = 1, and opposite. Logged in user's ID is $this->user->id. How to group all messages from one user and display only one row, even those I sent. Like you've got on FB. You have 10 messages from Derp Derpington, but only 1 is in the messages list: Derp Derpington (10).

Thanks in advance