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MathGroup Archive 1999

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Re: Fast List-Selection

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19922] Re: [mg19880] Fast List-Selection
  • From: Carl Woll <carlw at u.washington.edu>
  • Date: Tue, 21 Sep 1999 02:22:53 -0400
  • Organization: Physics Department, U of Washington
  • References: <199909192247.SAA12942@smc.vnet.net.>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Hans,

Here is one idea:

rep[ls_]:=Position[Partition[ls,7,1],{x_ ..}]

For a 10000 element random list of integers (0,1,2), it took less than a
second. It'll be interesting to see the other solutions.

Carl Woll
Physics Dept
U of Washington

Hans Havermann wrote:

> I have a list 's' composed of a large number of (small) integers. I wish to
> search this list for instances of 7 consecutive, identical elements.
>
> My approach is:
>
> Do[If[Count[t = Take[s, {i, i + 6}], t[[1]]] == 7,
>     Print[i]], {i, 1, Length[s] - 6}]
>
> Can anyone think of a *faster* way of doing this?







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