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MathGroup Archive 2004

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Re: Counting Runs

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51934] Re: [mg51890] Counting Runs
  • From: Selwyn Hollis <sh2.7183 at misspelled.erthlink.net>
  • Date: Fri, 5 Nov 2004 02:17:54 -0500 (EST)
  • References: <200411040650.BAA18131@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Greg,

The following seems to work pretty well:

   runscount[lst_?VectorQ] :=
     Module[{elems, flips, counts},
       elems = Union[lst];
       flips = Cases[Partition[lst, 2, 1], {x_, y_} /; x =!= y];
       counts = {#, Count[Most[flips], {#, _}]} & /@ elems;
       {x1, x2} = Last[flips];
       counts /. {{x1, y_} -> {x1, y+1}, {x2, y_} -> {x2, y+1}}]

Example:

  Table[Random[Integer, {1, 5}], {20}]
  runscount[%]

      {2, 2, 3, 1, 3, 2, 2, 3, 1, 1, 2, 3, 1, 1, 3, 1, 1, 2, 2, 2}

      {{1, 4}, {2, 4}, {3, 5}}


-----
Selwyn Hollis
http://www.appliedsymbols.com
(edit reply-to to reply)


On Nov 4, 2004, at 1:50 AM, Gregory Lypny wrote:

> Looking for an elegant way to count runs to numbers in a series.
> Suppose I have a list of ones and negative ones such as
> 	v={1,1,1,-1,1,1,1,1,1,-1,-1,-1,-1,1}.
> I'd like to create a function that counts the number of runs of 1s and
> -1s, which in this case is 3 and 2.
>
> 	Greg
>
>


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