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Re: majority voting [message #65168 is a reply to message #65079]

Wed, 11 February 2009 14:03

ben.bighair
Messages: 221
Registered: April 2007

Senior Member

On Feb 11, 4:53 pm, Mort Canty <m.ca...@fz-juelich.de> wrote:
> ben.bighair schrieb:
>
>
>
>> On Feb 11, 11:14 am, mort canty <m.ca...@fz-juelich.de> wrote:
>>> Hi all,
>
>>> Given a 2-D array such as
>
>>> 0 1 1 2 1
>>> 0 2 1 1 1
>>> 1 0 2 2 1
>
>>> where the entries are labels, the columns represent items and the rows
>>> are voters, I want a IDL function that returns the majority vote labels.
>>> So here I should get
>
>>> 0 ? 1 2 1
>
>>> as output, where ? = "don't care". There must _not_ be a loop over
>>> columns. I've got a clumsy solution, but I'm sure there's an elegant one
>>> somewhere?
>
>> Hi,
>
>> This is incomplete as it doesn't flag the "don't care" crowd. I can't
>> noodle that part out without column looping. Looping would make it
>> easy to use something like...
>
>> for i = 0, ncol-1 do dontCare[i] = ARRAY_EQUAL(votes[i,*],votes[i,0])
>
>> but by your rules, that is out of bounds.
>
>> ***BEGIN
>> x=[[0,1,1,2,1],$
>> [0,2,1,1,1],$
>> [1,0,2,2,1]]
>> sz = SIZE(x, /DIM)
>> votes = [[TOTAL(x EQ 0, 2)],$
>> [TOTAL(x EQ 1, 2)], $
>> [TOTAL(x EQ 2, 2)]]
>> mx = MAX(votes, mxIdx,dim = 2)
>> majority = (array_indices(sz, mxIdx, /dim))[1,*]
>> print, majority
>> ***END
>
>> Cheers,
>> Ben
>
> Thanks Ben. What I meant by "don't care" is that I don't care which of
> the labels that got equal votes is output. I think my solution is
> essentially the same as yours, certainly not more elegant:
>
> function majority_vote, A, num_labels
> n = n_elements(A[*,0])
> B = intarr(n,num_labels)
> for i=0,num_labels-1 do begin
> C = A*0
> idx = where(A eq i,count)
> if count gt 0 then C[idx] = 1
> B[*,i] = total(C,2)
> endfor
> void = max(B,labels,dimension=2)
> return, labels/n
> end
>
> I was probably hoping for some HISTOGRAM magic :-)
> Mort

Oooo. Histogram... well my mojo just isn't working that way today.
But deep inside Jean's addition is sort_nd (I had never heard of it
before - slick!) which has a histogram *with* reverse indices. Double
the mojo!

Cheers,
Ben

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[Message index]

		majority voting By: Mort Canty on Wed, 11 February 2009 08:14
		Re: majority voting By: Allan Whiteford on Fri, 13 February 2009 01:31
		Re: majority voting By: David Fanning on Sat, 14 February 2009 08:44
		Re: majority voting By: JD Smith on Thu, 12 February 2009 14:45
		Re: majority voting By: Foldy Lajos on Thu, 12 February 2009 12:47
		Re: majority voting By: David Fanning on Thu, 12 February 2009 12:11
		Re: majority voting By: pgrigis on Thu, 12 February 2009 11:58
		Re: majority voting By: JD Smith on Thu, 12 February 2009 10:49
		Re: majority voting By: Mort Canty on Thu, 12 February 2009 07:45
		Re: majority voting By: JD Smith on Thu, 12 February 2009 07:08
		Re: majority voting By: David Fanning on Thu, 12 February 2009 05:43
		Re: majority voting By: Allan Whiteford on Thu, 12 February 2009 04:17
		Re: majority voting By: Mort Canty on Thu, 12 February 2009 01:15
		Re: majority voting By: JD Smith on Wed, 11 February 2009 15:20
		Re: majority voting By: ben.bighair on Wed, 11 February 2009 14:03
		Re: majority voting By: Allan Whiteford on Mon, 16 February 2009 04:11

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