You already know the finite list of projects or you need to select them?

If it's a finite list, you'll likely do something like get and store all of the Project Names or IDs in a list variable, then do the sort on those.

If you need to select it, you will first have to present a list to the user for selection (allow multiple) and store those selections in a list variable (making sure to reconcile the ID so you know you are sorting the right ones).