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Re: Segregating data in bimodal distribution [message #77116]

Sun, 07 August 2011 07:01

ben.bighair
Messages: 221
Registered: April 2007

Senior Member

Hi,

On 8/3/11 11:37 AM, Jeremy Bailin wrote:
> On 8/3/11 8:35 AM, Eric Hudson wrote:
>> Hi,
>>
>> Is anyone aware of an IDL implemented algorithm for segregating data
>> in a bimodal distribution into two groups?
>>
>> My data is such that I could do it manually (make a histogram, decide
>> on a threshold between the two peaks in the histogram, then pull out
>> the data above and below that into two separate groups). There isn't
>> a true gap between the two peaks, but they are pretty well separated.
>> The part which is non-obvious to me is to how to programmatically
>> choose the threshold value. And since I have to do this on many data
>> sets, where the threshold is going to be different for each, I prefer
>> to not do it manually.
>>
>> Thanks,
>> Eric
>>
>> PS In searching I found something called the KMM algorithm which
>> seems like it would work, but I haven't found code for it.
>
> Are the peaks well-represented by a known function (e.g. Gaussian)? If
> so, you could fit a bimodal Gaussian/whatever to the distribution and
> use the parameters of the fit to determine when the total is dominated
> by one or the other peak.

A while back I translated some MatLab code to do this sort of thing. I
never got it to run very fast but it seemed to do pretty well. If I
rightly recall, I think it performed well when the peaks overlapped a lot.

You can find a copy of it here...

http://dl.dropbox.com/u/8433654/mb_mixg.pro

Note there are some obscure references and an example routine...

IDL> .compile mb_mixg
IDL> example
Threshold Selected = 132.47748

Cheers,
Ben

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[Message index]

		Re: Segregating data in bimodal distribution By: ben.bighair on Sun, 07 August 2011 07:01
		Re: Segregating data in bimodal distribution By: Jeremy Bailin on Wed, 03 August 2011 08:37
		Re: Segregating data in bimodal distribution By: Eric Hudson on Wed, 10 August 2011 04:59
		Re: Segregating data in bimodal distribution By: wulf.hendrik on Wed, 22 February 2017 06:30

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