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MathGroup Archive 2007

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Re: Iterate through a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76926] Re: [mg76886] Iterate through a list
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Wed, 30 May 2007 05:19:06 -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........

I'm not quite sure I understand your intent, First/@{{1,0},...} will  
get you a list of the numbers.

counts[lst_]:=Module[{items=Union[lst]},Transpose[{items,Count[lst,#] 
&/@items}]]

will get you a list of the numbers and their frequencies.

Regards,

Ssezi


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