Re: Re: Counting Runs
- To: mathgroup at smc.vnet.net
- Subject: [mg51993] Re: [mg51934] Re: [mg51890] Counting Runs
- From: DrBob <drbob at bigfoot.com>
- Date: Sat, 6 Nov 2004 02:08:39 -0500 (EST)
- References: <200411040650.BAA18131@smc.vnet.net> <200411050717.CAA06890@smc.vnet.net>
- Reply-to: drbob at bigfoot.com
- Sender: owner-wri-mathgroup at wolfram.com
I timed the posted methods except Andrzej's -- it's the only one that works only for +1/-1 data -- plus a couple of my own that I haven't posted. David Park's method seems the same as the fastest method, hanlon3. I modified all methods to return a pair {x, number of runs in x} for each x in the data.
Two of Bob Hanlon's methods beat all the rest of us -- but one of his is the slowest method, too.
I've posted a notebook at the Run Counts link at:
http://eclecticdreams.net/DrBob/mathematica.htm
Bobby
On Fri, 5 Nov 2004 02:17:54 -0500 (EST), Selwyn Hollis <sh2.7183 at misspelled.erthlink.net> wrote:
> 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
>>
>>
>
>
>
>
--
DrBob at bigfoot.com
www.eclecticdreams.net
- Follow-Ups:
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- From: Andrzej Kozlowski <akoz@mimuw.edu.pl>
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- References:
- Counting Runs
- From: Gregory Lypny <gregory.lypny@videotron.ca>
- Re: Counting Runs
- From: Selwyn Hollis <sh2.7183@misspelled.erthlink.net>
- Counting Runs