How to populate 2d-array from 3d array with page indices

Hi!

Please see my example below. I start with a non-scalar structure, which I concatenate into a 3d-array. I then find the minimum values and their indices in the 3rd dimension using 'min'. Then, from a second array of exactly the same size, I want to extract a new array with entries corresponding to indices in the min value indices from the other array. I can do this perfectly well with the loop below, but doing it by vectorization would be twice as fun :)

The values in 'b' array is chosen to better illustrate the problem, as it is directly related to the 'pageIdx' array.

BR Andreas.

    s(1).f=rand(2);
    s(2).f=rand(2);
    s(3).f=rand(2);
    a=cat(3,s.f);

    b=ones(2,2,3);
    b(:,:,2)=2;
    b(:,:,3)=3;

    [minVals,pageIdx]= min(a,[],3)

    bSize = size(b); nRows = bSize(1); nCols = bSize(2);

    bMinVals = zeros(nRows,nCols);
    for iRow = 1:nRows
        for jCol = 1:nCols
            bMinVals(iRow,jCol)=b(iRow,jCol,pageIdx(iRow,jCol));
        end
    end

    bMinVals == pageIdx

Answer 1

[Guillaume]

a = rand(2, 2, 3);
b = ones(2, 2, 3); b(:, :, 2) = 2; b(:, :, 3) = 3; 
b= -b; %to differentiate from PageIdx

[minVals, PageIdx] = min(a, [], 3);
[r, c] = ndgrid(1:size(b, 1), 1:size(b, 2));
bMinVals = reshape(b(sub2ind(size(b), r(:), c(:), PageIdx(:))), size(b, 1), [])
isequal(bMinVals, -PageIdx)