Maximizing along n-1 dimensions of an n-dimensional array without a for loop

Question

Brandon 2021-10-12

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https://ww2.mathworks.cn/matlabcentral/answers/1562311-maximizing-along-n-1-dimensions-of-an-n-dimensional-array-without-a-for-loop

评论： Jan 2021-10-13

I have an n-dimensional array, VV, which I would like to maximize along all dimensions for each element in the first dimension. I would also like to obtain the associated linear indices so that I can evaluate related arrays at those locations. I have to do this a large amount of times, so I need to figure out a way to do this without a for loop.

Here is an example for an n=3 dimensional array, but with a loop:

VV=rand(10,10,10);

for ii=1:size(VV,1)

Vtemp = squeeze(VV(ii,:,:));

[V(ii) I(ii)] = max(Vtemp(:));

end

[~,ind] = ismember(V,VV);

Any help would be appreciated.

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Answer 1

Jan 2021-10-12

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https://ww2.mathworks.cn/matlabcentral/answers/1562311-maximizing-along-n-1-dimensions-of-an-n-dimensional-array-without-a-for-loop#answer_807236

编辑：Jan 2021-10-12

在 MATLAB Online 中打开

VV = rand(8, 9, 10);
for ii = 1:size(VV,1)
  Vtemp          = squeeze(VV(ii, :, :));
  [V(ii), I(ii)] = max(Vtemp(:));
end
[~,ind] = ismember(V, VV);
ind
ind = 1×10
        1161          12         293        1004         415         746         307        1228         479         620
s = size(VV, 1);
W = reshape(VV, s, []);
[maxV, Index] = max(W, [], 2);
ind2 = sub2ind(size(W), 1:s, Index.')
ind2 = 1×10
        1161          12         293        1004         415         746         307        1228         479         620

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Brandon 2021-10-12

This works for me. Thanks so much!

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Answer 2

Steven Lord 2021-10-12

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1562311-maximizing-along-n-1-dimensions-of-an-n-dimensional-array-without-a-for-loop#answer_807296

在 MATLAB Online 中打开

VV=randi(1000, 5, 5, 5);
[values, locations] = max(VV, [], 1:ndims(VV)-1, 'linear');
check = [reshape(values, [], 1), reshape(VV(locations), [], 1)]
check = 5×2
   904   904
   984   984
   973   973
   981   981
   975   975