(50g) Removing Objects From Lists Quickly

[John Keith]

Thanks, David.

From my (limited) understanding of set theory, the difference function (as well as intersection and, of course, union) should eliminate any duplicates. Set functions in Mathematica work this way. All three of those functions in GoferLists return lists with duplicate objects in some circumstances. I believe that this behavior is erroneous. (Maybe not- see post #11 below.)

Along those lines, I also came up with a similar program for set intersection. It is also much faster than GoferLists' Intersect:

Code:


\<< SWAP DUP ROT LSORT LGRP DUP HEAD UNROT PICK3 OVER SIZE LMRPT LREPL SWAP MPOS LPICK
\>>

The order of commands may seem strange but gives correct results faster than any other program I could come up with. Others are encouraged to improve the code, and especially to test it for correctness.