Change Div Opacity

I’m adding a sub menu to my portfolio page that will allow a user to filter the types of projects they want to see, but I’m not really sure how to approach this. I have a variety of web design and motion graphics projects all on the same page, and I want the user to be able to “uncheck” one category or the other, and when they do, all the divs for the unchecked category will fade out. This is the page:

Does that make sense? What I’m thinking of doing is applying a unique ID to the different categories, then build a little JS that will change the opacity of those specific IDs somehow. I am not a JS ninja though, and I’m thinking there is probably a more efficient way.

Here’s an example of what I’m going for with the fading.