Somehow I lost the thing that groups running programs on the task bar.
I thought it might be a "Grouping Panel" but I get a polkit error when I tried to add that (the error only showed up the first time I tried to add it, subsequent times, the screen goes black for a few seconds but nothing happens).
Is there a way to edit a config file to add it back?

assuming you have the Task Manager widget/plasmoid installed right click on the task bar and select "Task Manager Settings" to change grouping options. If you don't have the Task Manager installed then install it.

fyi the taskbar rc file is /home/smiley/.kde[4]/share/config/ktaskbarrc

Thanks, I don't know how my task manager got lost but I added the widget and it is the way it was.