SharePoint 2013: Modify subject view to include a group by the category

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SharePoint2013

Hi,
I'm new to SP 2013, and I have been struggling with this.

I have a community site, and the subject view is almost what we want. The only thing we would like, is to have the topics grouped by the category.

So basically this

Category 1
topic a
Topic b

Category 2
Topic c

But I cannot figure out what I need to do, to make this small update.

doesn't anyone know how to do this?

Stuff like this used to be easy to do in SP2010/07 but this is frustrating.

Thanks!