On Jan 25, 7:49 pm, Ed Hyer <ejh...@gmail.com> wrote:
> On Jan 25, 12:47 pm, Ed Hyer <ejh...@gmail.com> wrote:
>
>> 1) The number of different values in the matched grids;
>> 2) The mode, that is, the frequency of the most common value.
>
> So, what I ended up with was something like this:
>
> allgrids=[[[grid1]],[[grid2]],etc.]
> matchcount=allgrids *0b; initialize
> for i1=0,ngrids-1 do for i2=0,ngrids-1 do matchcount[*,*,i1] +=
> (allgrids[*,*,i1] eq allgrids[*,*,i2])
> magnitude_of_mode = max(matchcount,dim=3,imode)
> value_of_mode = allgrids[imode]
>
> So 2 for-loops still needed, but across the shortest dimension.
>
> --Edward H.
Here's a pure IDL no-loop solution that uses... <drum roll>... the
combination of VALUE_LOCATE and HISTOGRAM! (tell me you didn't see
that coming).
; some sample data
grid1 = [[1., 0, -10, 1.],[-5, -10, 9, 8],[0, 1, 2, 3]]
grid2 = [[1., 9, 8, 2],[-5, 0, 2, 3],[0, 1, 2, 3]]
grid3 = [[-10, 8, 9, 2],[-5, -10, 1, 3],[0, 1, 2, 3]]
grid4 = [[0, 9, 8, 2],[-10, 2, 2, 2],[0, 1, 2, 3]]
grid5 = [[1., -2, -20, 2],[-5, 2, 2, 8],[0, 1, 2, 3]]
allgrids = [[[grid1]],[[grid2]],[[grid3]],[[grid4]],[[grid5]]]
gridsize=size(allgrids,/dimen)
npix = gridsize[0]*gridsize[1]
uniqvals = allgrids[uniq(allgrids,sort(allgrids))]
nuniq = n_elements(uniqvals)
; map values into their index in uniqvals so we only need to
; deal with integers
mappedgrids = value_locate(uniqvals, allgrids)
; now we can use histogram!
; first give each pixel its own increment so that the histogram for
; the pixels run from 0..nuniq-1, nuniq..2*nuniq-1, etc.
pixincrement = ((lindgen(gridsize[0]) # replicate(1,gridsize[1])) + $
(lindgen(gridsize[1]) ## replicate(1,gridsize[0]) * gridsize[0])) *
nuniq
; now histogram everything
gridhist = reform(histogram(mappedgrids + rebin
(pixincrement,gridsize), $
bin=1, min=0, max=npix*nuniq-1), nuniq, gridsize[0], gridsize[1])
; get the mode and value out of the histogram, for each pixel
magnitude_of_mode = max(gridhist, dim=1, imode)
value_of_mode = uniqvals[imode - pixincrement]
IDL> print, magnitude_of_mode
3 2 2 4
4 2 3 2
5 5 5 5
IDL> print, value_of_mode
1.00000 9.00000 8.00000 2.00000
-5.00000 -10.0000 2.00000 3.00000
0.00000 1.00000 2.00000 3.00000
-Jeremy.
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