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MathGroup Archive 2007

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Re: Iterate through a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76931] Re: [mg76886] Iterate through a list
  • From: János <janos.lobb at yale.edu>
  • Date: Wed, 30 May 2007 05:21:41 -0400 (EDT)
  • References: <200705290902.FAA03917@smc.vnet.net>

On May 29, 2007, at 5:02 AM, Nick Hoffman wrote:

> Hello! I'm (somewhat) new to Mathematica and I  need help to iterating
> through a list and counting the occurrence of a number.
>
> My list looks like:
>
> {{1,0},{1,1},{2,x+x^2+x^4},{2,1+x+x^2+x^4},{4,x+x^2},{4,1+x+x^2},
> {4,x+x^4},{4,1+x+x^4},{4,x^2+x^4},{4,1+x^2+x^4},{4,x^3+x^4},{4,1+x^3=

> +x^4},{4,x+x^2+x^3+x^4},{4,1+x+x^2+x^3+x^4},{5,x+x^3},{5,1+x+x^3},
> {5,x^2+x^3},{5,1+x^2+x^3},{5,x+x^3+x^4},{5,1+x+x^3+x^4},{5,x^2+x^3
> +x^4},{5,1+x^2+x^3+x^4},{8,x},{8,x^2},{8,x^3},{8,x^4},{8,1+x},{8,1
> +x^2},{8,1+x^3},{8,x+x^2+x^3},{8,1+x+x^2+x^3},{8,1+x^4}}
>
>
>
> The number that I would need to keep track of is the first in each 
> sub-
> list.
>
> So for the first couple {{1,0},{1,1},{2,x+x^2+x^4},{2,1+x+x^2+x^4},
> {4,x
> +x^2},........
>
> I would need to keep track of 1,1,2,2,4........
>
> It will not always be 1,2,4,5,8's.  The numbers may be completely
> different on each pass.  Each sublist may be composed of more items
> but the number that I need to keep track of will always be the 1st in
> the sub-list.  Any help or suggestions that you can give me will be
> greatly appreciated.  Thanks so much!


Here is a newbie approach for this concrete list:

In[2]:=
First /@ lst
Out[2]=
{1, 1, 2, 2, 4, 4, 4, 4, 4,
   4, 4, 4, 4, 4, 5, 5, 5, 5,
   5, 5, 5, 5, 8, 8, 8, 8, 8,
   8, 8, 8, 8, 8}

J=E1nos


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