Select items into categories

Hi.

Let's say, I have a large set of circles with diameters ranging from 0.0 to 1. I would like to select them into categories, e.g., circles with diameter 0.01-0.1 go to category A, 0.11-0.2 - category B, etc. How do I perform such a selection - preferably not only with circles, but with any sort of data that I would like to divide into sub-categories?

Thanks beforehand!

I.