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MathGroup Archive 1997

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Re: selecting from lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg6222] Re: [mg6184] selecting from lists
  • From: Jens Potschadtke <Jens.Potschadtke at stud.uni-erlangen.de>
  • Date: Fri, 28 Feb 1997 03:21:41 -0500
  • Organization: Institute for Biomedical Engineering at the FAU Erlangen
  • Sender: owner-wri-mathgroup at wolfram.com

Frans Martens wrote:
> 
> Murray wrote:
> 
> The problem: given an arbitrary list v and a list b of the same
> length, whose entries are all Boolean (True or False), construct a
> function s[v, b] whose result is a list consisting only of those
> entries of v for which the corresponding entries in b are True.  For
> example,
> 
>    v = {3, 82, 7, -12, 5};
>    b = {False, True, True, False, False};
>    s[v, b]
>    {82, 7}
> 

[...]
> 
> Yes, there is a more direct way! I have added some computations.
> 
>    t[v_,b_] := Cases[Transpose[{v,b}],{a_,True}:>a]
> 

You can also give a try to the solution of the wolfram-folks,
because there exists a predefined function:

<<Statistics`DataManipulation`
BooleanSelect[v,b]

----
Jens Potschadtke
Institute for Biomedical Engineering at the University of Erlangen
(Germany)
mailto:Jens.Potschadtke at stud.uni-erlangen.de
http://www.uni-erlangen.de/~sz0438/


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