       Re: Iterate through a list

• To: mathgroup at smc.vnet.net
• Subject: [mg76904] Re: [mg76886] Iterate through a list
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Wed, 30 May 2007 05:07:40 -0400 (EDT)

```data = {{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}};

fe = First /@ data

{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}

{#, Count[fe, #]} & /@ Union[fe]

{{1, 2}, {2, 2}, {4, 10}, {5, 8}, {8, 10}}

Alternatively,

{#[], Length[#]} & /@ Split[Sort[fe]]

{{1, 2}, {2, 2}, {4, 10}, {5, 8}, {8, 10}}

The Sort used above is not needed if the first element of your data is always sorted (as in your example).

Bob Hanlon

---- Nick Hoffman <hoffmannick at gmail.com> 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!
>

```

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