generative modeling for Rhino
You are looking for "CreateSet"
edit: sorry. Misread your post. If you can sort the List, then pairs occur on consequitve indices. You can shift the list by one and compare this with the original. If it is a pair both list items are equal. You can use this boolean pattern to cull one of the lists.
I got two ways copied out of my libary.
Please ask any questions if you do not understand how the file works. It is a very useful way of how to create paths with equal informations. You can sort any type of geometry with this.
Thanks for all the input. I really appreciate it!