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MathGroup Archive 1996

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Re: How do I use Select[list,condition]?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4546] Re: How do I use Select[list,condition]?
  • From: Nate Brixius <brixius at cs.uiowa.edu>
  • Date: Wed, 7 Aug 1996 04:17:52 -0400
  • Organization: The University of Iowa
  • Sender: owner-wri-mathgroup at wolfram.com

Jason Welter wrote:
> 
> I have a list that looks like:
> 
> data = {{1,1,a,4,5,6},{2,1,a,2,3,4},{3,1,a,7,8,9},
>                {1,2,b,4,5,6},{2,2,b,2,3,4},{3,2,b,7,8,9},
>                {1,3,c,4,5,6},{2,3,c,2,3,4},{3,3,c,7,8,9}}
> 
> and I want to pick out the lists that have a 2 as the second element
> of the list.  I tried something like:
> 
> data1 = Select[data,data[[#,2]]==2];
> 
> but this doesn't work.  How do I do it?
Try the following:

data = {{1,1,a,4,5,6},{2,1,a,2,3,4},{3,1,a,7,8,9},
               {1,2,b,4,5,6},{2,2,b,2,3,4},{3,2,b,7,8,9},
               {1,3,c,4,5,6},{2,3,c,2,3,4},{3,3,c,7,8,9}}
data1 = Select[data,(#[[2]]==2)&]

Output:
Out[58]=
{{1, 1, a, 4, 5, 6}, {2, 1, a, 2, 3, 4}, {3, 1, a, 7, 8, 9}, 
 
  {1, 2, b, 4, 5, 6}, {2, 2, b, 2, 3, 4}, {3, 2, b, 7, 8, 9}, 
 
  {1, 3, c, 4, 5, 6}, {2, 3, c, 2, 3, 4}, {3, 3, c, 7, 8, 9}}
Out[59]=
{{1, 2, b, 4, 5, 6}, {2, 2, b, 2, 3, 4}, {3, 2, b, 7, 8, 9}}

I hope this helps.

Nate

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