Compare matrix element without loops

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shdotcom shdotcom 2019-5-4

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https://ww2.mathworks.cn/matlabcentral/answers/460214-compare-matrix-element-without-loops

评论： dpb 2019-5-4

采纳的回答： dpb

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Hi,

Is there any way to get same result without using loops?

G = [5 8; 8 5; 3 9; 7 3; 1 4; 5 10; 6 7; 4 10; 4 7; 1 6];
n = 2;
nG = size(G,1);   
for ii=1:nG
   zz =1;
   isDom = [];
   for kk=1:n
        for jj=1:nG
            if ii ~= jj
                isDom(zz) = G(ii,kk) <  G(jj,kk);
                zz = zz +1;
            end
        end
   end        
  R(ii) = sum(isDom==1);
end

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Answer 1

dpb 2019-5-4

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编辑：dpb 2019-5-4

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Not w/o zero loops, think not, but can reduce to one...

idx=1:nG;            % working index array for element logical lookup/exclusion
R=zeros(nG,1);       % preallocate
for i=1:nG
  isDom=(G(i,:)-G(idx~=i,:));
  R(i)=sum(isDom(:)<0);
end

You can eliminate the intermediate isDom temporary if desired..."exercise for the student" :)

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shdotcom shdotcom 2019-5-4

Thank you

dpb 2019-5-4

You can also, of course, remove the explicit loop via arrayfun, but the loop is still there and resulting code is somewhat obfuscated and may well be slower, besides...

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