Re: Intersection @ Complement

*To*: mathgroup at smc.vnet.net*Subject*: [mg58116] Re: Intersection @ Complement*From*: David Bailey <dave at Remove_Thisdbailey.co.uk>*Date*: Sun, 19 Jun 2005 03:43:19 -0400 (EDT)*References*: <d90tcg$99f$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Zak Seidov wrote: > Some crazy thing Mmca does with > Intersection/Complement: > > s1={1,2,5,7,4,4,1};s2={1,6,3,5,7,7,1,6}; > Intersection[s1,s2] > {1,5,7} (* not {1,1,5,7} ?!*) > Complement[s1,s2] > {2,4} (* not {2,4,4} ?!*) > Complement[s2,s1] > {3,6} (* not {3,6,6,7} ?!*) > > Interestingly, in both cases Mmca Help > says that the result is SORTED list, > while actually it's UNION not SORT that works?! > And note that in the last case 7 is absent at all ?! > what d'u think about this? thanks a lot, zak > These are SET operations - they are meant to work on lists of distinct objects - if you give them lists with repeats, the arguments are subjected to Union first. David Bailey http://www.dbaileyconsultancy.co.uk