Scrambling rows of data while keeping some rows grouped to one another

I am currently working a project that requires me to scramble data by rows. Here is an image to help with my explanation: http://i.imgur.com/vUyoe.jpg

You will see [number][letter] columns (3B, 4A...) are paired with [number] columns directly to the right. So 3B can be subdivided into 3B - 1, 3B -2, and so on. Or, as you can see more fully, 4A can be subdivided from 1 - 8.

What I am trying to do is randomize all the 1A's, 2A's, etc. but also keep them with their respective subdivisions.

So for example: my randomization may end up producing 2A - 2, 4B - 8, 1A - 1, and so on. I am slightly familiar with the rand() function, but it doesn't seem to help me in this case.

Thanks for the help!