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MathGroup Archive 2007

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Re: Iterate through a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76961] Re: Iterate through a list
  • From: Szabolcs <szhorvat at gmail.com>
  • Date: Wed, 30 May 2007 05:37:15 -0400 (EDT)
  • Organization: University of Bergen
  • References: <f3gqtq$42r$1@smc.vnet.net>

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!
> 

Try to avoid explicit iteration in Mathematica. If the list is called 
data, try

First /@ data

Count[%, 3]

to count the occurrences of the number 3.


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