Displaying grouped view of node comments in a view listing nodes
So far I've only found a couple way of doing this, non of them seem very elegant.
If you choose the group by option, it does indeed duplicate all of the fields with the exception of the one you are grouping by. If you omit all the fields form the display, then click on the the grouped field and "rewrite the output" you can use tokens to output all of the fields, and they only display once. Unfortunately, this  kinds defeats the purpose of using fields in the first place. The other option is to use the node or teaser view, and make alterations to node.tpl.php and comment.tpl.php as needed ....