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  • To: mathgroup at smc.vnet.net
  • Subject: [mg87729] Select from list
  • From: Steve Gray <stevebg at roadrunner.com>
  • Date: Wed, 16 Apr 2008 05:04:08 -0400 (EDT)

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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