Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2004
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2004

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Re: Counting Runs

  • To: mathgroup at smc.vnet.net
  • Subject: [mg51995] Re: [mg51934] Re: [mg51890] Counting Runs
  • From: János <janos.lobb at yale.edu>
  • Date: Sat, 6 Nov 2004 02:08:47 -0500 (EST)
  • References: <200411040650.BAA18131@smc.vnet.net> <200411050717.CAA06890@smc.vnet.net> <opsg0lmi1fiz9bcq@monster.cox-internet.com> <opsg0pe8woiz9bcq@monster.cox-internet.com>
  • Sender: owner-wri-mathgroup at wolfram.com

It must be machine or OS dependent.

I re-discovered Hanlon3 method :) and  ran it with Bobby's newest.  I 
don't have Bobby's data so I generated random didgits in the 0-9 range

Here are the results:

In[28]:=
v = Table[Random[Integer,
      {0, 9}], {i, 1, 10^7}];

In[29]:=
Timing[({First[#1],
      Length[#1]} & ) /@
    Split[Sort[First /@
       Split[v]]]]
Out[29]=
{35.58*Second, {{0, 898901},
    {1, 899397}, {2, 901191},
    {3, 899449}, {4, 900824},
    {5, 900262}, {6, 899338},
    {7, 900293}, {8, 900196},
    {9, 901311}}}

In[32]:=
Timing[({First[#1],
      Length[#1]} & ) /@
    Split[Sort[Split[v][[All,
       1]]]]]
Out[32]=
{38.67999999999998*Second,
   {{0, 898901}, {1, 899397},
    {2, 901191}, {3, 899449},
    {4, 900824}, {5, 900262},
    {6, 899338}, {7, 900293},
    {8, 900196}, {9, 901311}}}

My machine is a 1.25Ghz G4 with 2G Ram and with OSX 10.3.5.

János
On Nov 5, 2004, at 7:38 PM, DrBob wrote:

> I found an even faster (rather obvious) solution:
>
> hanlonTreat[v_] := {First@#, Length@#} & /@ Split@Sort[Split[v][[All, 
> 1]]]
>
> It about 80% faster than hanlon4.
>
> Bobby
>
> On Fri, 05 Nov 2004 17:16:56 -0600, DrBob <drbob at bigfoot.com> wrote:
>
>> 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
>
>

-------------------------------------------------------------------
János Löbb
Yale University School of Medicine
Department of Pathology
Phone: 203-737-5204
Fax:      203-785-7303
E-mail: janos.lobb at yale.edu


  • Prev by Date: Re: Re: Problems about Graphics
  • Next by Date: Re: Re: Counting Runs
  • Previous by thread: Re: Re: Counting Runs
  • Next by thread: Re: Re: Counting Runs