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Re: Counting number of numbers in a large list between two valus

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  • Subject: [mg114544] Re: Counting number of numbers in a large list between two valus
  • From: Lyle Gordon <lgordon at gmail.com>
  • Date: Tue, 7 Dec 2010 06:46:51 -0500 (EST)

Again, thanks to everyone who responded.

After some playing around it seems that since I need to run the code a
number of times on the same set of data and my ranges only have a certain
degree of precision this code might be faster:

binwidth = 10^-5;
min = Floor[Min[data], binwidth];
max = Ceiling[Max[data], binwidth];
binneddata = BinCounts[data, {min, max, binwidth}];
tallydata4[{x1_, x2_}] :=
 Total[Take[
   binneddata, {(x1 - min)/binwidth + 1, (x2 - min)/binwidth}]]

Thanks,
Lyle

--
Lyle Gordon
Department of Materials Science and Engineering
Northwestern University

2220 Campus Drive
Evanston, IL 60208

Tel: (847) 491-3584
Mobile: (847) 400-4071
lgordon at u.northwestern.edu


On Mon, Dec 6, 2010 at 11:27 AM, Lyle Gordon <lgordon at gmail.com> wrote:

> Thanks everyone for your responses, it seems like Carl's and Fred's method
> with Total-Unitize-Clip is the fastest.
>
> Thanks very much,
> Lyle
>
> --
> Lyle Gordon
> Department of Materials Science and Engineering
> Northwestern University
>
> 2220 Campus Drive
> Evanston, IL 60208
>
> Tel: (847) 491-3584
> Mobile: (847) 400-4071
> lgordon at u.northwestern.edu
>
>
>
> On Mon, Dec 6, 2010 at 5:33 AM, Leonid Shifrin <lshifr at gmail.com> wrote:
>
>> Hi Lyle,
>>
>> Sorry - I misunderstood the problem. I thought you meant the positional
>> arrangement
>> of the numbers.  Since you seem to be getting plenty of good answers, I
>> will not attempt
>> to correct myself with more code.
>>
>>
>> Regards,
>> Leonid
>>
>>
>> On Mon, Dec 6, 2010 at 5:57 AM, Lyle <lgordon at gmail.com> wrote:
>>
>>> Dear Listers,
>>>
>>> I have a large (5-20million) one dimensional list of real numbers and
>>> I want to count the number of entries in the list that lie between 2
>>> specific values (x1, x2). I need to run the function for a number of
>>> different ranges.
>>>
>>> ie. number of list entries (l), where x1 <= l <= x2
>>>
>>> I've tried:
>>>
>>> tallydata[{x1_, x2_}] := Count[data, x_ /; x1 <= x <= x2]
>>>
>>> that takes about 3-4 seconds
>>>
>>> and
>>>
>>> tallydata[{x1_, x2_}] := Length[Select[data, x1 <= # <= x2 &]]
>>>
>>> which takes a little bit longer.
>>>
>>> The best I've managed is (this last one might be off by 1 or 2 but
>>> this doesn't really matter to me):
>>>
>>> sorteddata = Sort[data];
>>> nf = Nearest[sorteddata];
>>> tallyrange[{x1_, x2_}] :=
>>>  First[Position[sorteddata, First[nf[x2]]]] -
>>>  First[Position[sorteddata, First[nf[x1]]]]
>>>
>>> which takes between 1 and 2 seconds but I was hoping there might be a
>>> faster way to do this?
>>>
>>> Any help would be great!
>>>
>>> Thanks,
>>> Lyle Gordon
>>>
>>> Northwestern University
>>>
>>>
>>
>


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