A long time ago I wrote about adding Column Groups to Interactive Reports (IR) in APEX: http://www.talkapex.com/2009/03/column-groups-in-apex-interactive.html I created a new dynamic action plugin to do column grouping in APEX which can be downloaded here. Please read the help text in the plugin for full instructions on how to use it. Once integrated it should look like:

I also added additional JS debugging information. If you run your application in debug mode and look at the console you'll notice the following log information:

The additional logging is using the console logger wrapper that wrote: http://www.talkapex.com/2010/08/javascript-console-logger.html If you're writing your own plugins I suggest using it to instrument your code. It helped me debug some of my JavaScript issues while developing this plugin.