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Re: Select from list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87756] Re: [mg87729] Select from list
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Wed, 16 Apr 2008 06:52:07 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

ptX = {{1, 2, 3, 4}, {1, 2, 3, 5}, {1, 2, 4, 5}, {1, 3, 4, 5}, {2, 3, 4, 5}};

If the sublists are always ordered

Position[ptX, {___, 2, ___, 3, ___}] // Flatten

{1,2,5}

If not, sort first

Position[Sort /@ ptX, {___, 2, ___, 3, ___}] // Flatten

{1,2,5}


Bob Hanlon

---- Steve Gray <stevebg at roadrunner.com> wrote: 
> I have a list like this:
> 
> ptX=
> {{1, 2, 3, 4}, {1, 2, 3, 5}, {1, 2, 4, 5}, {1, 3, 4, 5}, {2, 3, 4, 5}}
> 
> and I want a list pointing to all the sublists above that contain both
> a 2 and a 3. In this example I would get {1,2,5}. The best solution I
> have, with more generality, is:
> 
> va = 2;
> vb = 3;
> za = Map[Cases[#1, va]&, ptX] /. {} -> {0}
> zb = Map[Cases[#1, vb]&, ptX] /. {} -> {0}
> Flatten[Position[za*zb, {va*vb}]]
> 
> which gives
> 
> {{2}, {2}, {2}, {0}, {2}}
> {{3}, {3}, {0}, {3}, {3}}
> {1, 2, 5}. 
> 
> (This doesn't work if va or vb is zero. That's ok.)
> There's probably a better way. Anyone? Thank you.
> 
> Steve Gray
> 



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