The syntax mapping(x, y) * visual(Lines) passing vectors directly is already taken for pre-grouped data, but maybe it is more natural to use it for the usecase you are suggesting. Pre-grouped data should have to be signaled explicitly by the user (as was the case in a previous version). This will require a little bit of thought, but it’s an interesting point to consider.
PS sorry for hijacking the thread on Beautiful Makie with this side discussion