Re: List complement operator
- To: mathgroup at smc.vnet.net
- Subject: [mg84983] Re: [mg84950] List complement operator
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Tue, 22 Jan 2008 01:48:52 -0500 (EST)
- Reply-to: hanlonr at cox.net
a = {1, 1, 1, 2, 3, 3, 4, 5, 5, 5, 2, 6, 7, 7};
b = {1, 2, 2, 3, 4, 7, 8};
Fold[Delete[#1, Position[#1, #2][[1, 1]]] &, a,
Fold[DeleteCases[#1, #2] &, b, Complement[b, a]]]
{1,1,3,5,5,5,6,7}
Bob Hanlon
---- zac <replicatorzed at gmail.com> wrote:
> Dear group,
>
> I'm loooking for an elegant and efficient way to subtract a list (not
> a set) from an other one.
>
> a = {1, 1, 1, 2, 3, 3, 4, 5, 5, 5, 2, 6, 7, 7};
> b = {1, 2, 2, 3, 4, 7, 8};
>
> Complement[a,b] returns {5, 6}, as expected. However I would like to
> treat each entry as a discrete element, therefore my target result is:
> {1, 1, 3, 5, 5, 5, 6, 7}. Union can not be used, although Sort is
> allowed (ie. whether the result is sorted or not is of no concern).
> Any idea?
>
> Istvan Zachar
>