Re: Removing list elements in x by list y

*To*: mathgroup at smc.vnet.net*Subject*: [mg131177] Re: Removing list elements in x by list y*From*: Dana DeLouis <dana01 at icloud.com>*Date*: Sat, 15 Jun 2013 04:25:48 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net

> I wish to "subtract" y from x, i.e. remove exactly the elements in x Hello. I may be wrong, but if you have 10 each of everything, and wanted to subtract 8 of each item, you should be left with 2 items of each. x=Table[{a,b,c,d},{10}]//Flatten//Sort; y=Table[{a,b,c,d},{8}]//Flatten//Sort; Select[x,FreeQ[y,#]&] {} Cases[x,_?(FreeQ[y,#]&)] {} Pick[x,FreeQ[y,#]&/@x] {} Delete[x,Flatten[Map[Position[x,#]&,y],1]] {} x/.a_/;MemberQ[y,a]->Sequence[] {} Delete[x,Flatten[Position[x,#]&/@y,1]] {} DeleteCases[x,Alternatives@@y] {} Select[x,!MemberQ[y,#]&] {} I believe the answer should be: Fold[DeleteCases[#1,#2,1,1]&,x,y] {a,a,b,b,c,c,d,d} On Thursday, June 13, 2013 2:31:35 AM UTC-4, Dr. Wolfgang Hintze wrote: > I have simple question. > > > > Given two lists > > > > x = {u, v, w, w, d}; > > y = {u, d}; > > > > I wish to "subtract" y from x, i.e. remove exactly the elements in x > > which belong to y giving > > > > x "-" y = {v,w,w} > > > > Complement[] gives instead {v,w}. > > Note that we are talking about lists rather than sets. > > > > I'm sure there is a simple standard command, but I can't find it. > > Can you? > > > > Regards, > > Wolfgang