| Re: Mode function for floating point arrays [message #85120 is a reply to message #85119] |
Mon, 08 July 2013 01:24   |
Rob Klooster
Messages: 18
Registered: February 2013
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Junior Member |
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On second thought, it will be more efficient to treat the array as a sparse array and use value_locate, as in David's article:
http://www.idlcoyote.com/code_tips/valuelocate.html
sortedarray = array[Sort(array)]
arrayenum = sortedarray[Uniq(sortedarray)]
mappedarray = Value_Locate(arrayenum, array)
hist = histogram(mappedarray, min=0)
mode = arrayenum[where(hist eq max(hist))]
Maybe you can update the uniq function to accept a value for epsilon to decide whether two floating values are equal or not.
Regards,
Rob.
> Op maandag 8 juli 2013 10:01:16 UTC+2 schreef Rob Klooster het volgende:
> Hi Matthew,
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> Histogram also works on floating point arrays, you just need to set the binsize:
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> hist = histogram(array, binsize=epsilon, locations=locations)
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> mode = locations[where(hist eq max(hist))]
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> Note that for small values of epsilon, the resulting histogram array can become very large.
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> Regards,
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> Rob.
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> Op vrijdag 5 juli 2013 20:55:23 UTC+2 schreef Matthew Argall het volgende:
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>> PEAMBLE:
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>> I need a function that finds the mode of a floating point array. I have read David Fanning's article about integer arrays
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>> http://www.idlcoyote.com/code_tips/mode.html
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>> From this article about majority voting, it seems like "Hist_ND" works for floating point values, but I have no experience with the magic of HISTOGRAM
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>> https://groups.google.com/forum/#!searchin/comp.lang.idl-pvw ave/Mode$20of$20a$20floating$20point$20array/comp.lang.idl-p vwave/YZK2ey-O5sE/9fLvx_AG2IAJ
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>> QUESTION:
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>> Here is my attempt. Can anyone make it better/faster?
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>> ;-----------------------------------------------------
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>> function mrmode, array, $
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>> EPSILON=epsilon
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>> compile_opt idl2
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>> ;Number of points in ARRAY
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>> npts = n_elements(array)
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>> ;Default value for EPSILON
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>> if n_elements(epsilon) eq 0 then epsilon = 1d-5
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>> ;[index, count] for keeping track of mode statistics
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>> mode_count = lonarr(2, npts)
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>> ;Store first ~unique number. Count the how many ~unique numbers there are.
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>> mode_count[*,0] = [0,1]
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>> nunique = 1
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>> ;Step through all points in ARRAY
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>> for i = 1, npts - 1 do begin
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>> match_found = 0
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>> ;Try to pair the new point with other mode candidates
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>> for j = 0, nunique - 1 do begin
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>> if array[i] gt array[mode_count[0,j]]-epsilon && $
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>> array[i] lt array[mode_count[0,j]]+epsilon $
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>> then begin
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>> mode_count[1,j] += 1
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>> match_found = 1
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>> endif
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>> endfor
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>> ;If no match was found, create a new mode candidate
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>> if match_found eq 0 then begin
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>> mode_count[*,nunique] = [i,1]
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>> nunique += 1
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>> endif
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>> endfor
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>> ;Get the mode
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>> void = max(mode_count[1,*], iMode)
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>> mode = array[mode_count[0,iMode]]
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>> return, mode
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>> end
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>> ;----------------------------------------------------------- ----------
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>> ;Example Program (IDL> .r mrmode) /////////////////////////////////////////
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>> ;----------------------------------------------------------- ----------
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>> array = [1.2, 0.1, 3.3, 0.1, 2.0, 3.3, 4.8, 1.2, 0.1, 0.1, 6.7, 3.3]
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>> mode = MrMode(array)
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>> print, FORMAT='(%"The mode is: %f")', mode
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>> end
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