How to check whether any two elements are equal or not in a Nx1 array in matlab?

Question

Swarnajyoti Mukherjee 2019-11-19

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https://ww2.mathworks.cn/matlabcentral/answers/491935-how-to-check-whether-any-two-elements-are-equal-or-not-in-a-nx1-array-in-matlab

评论： Swarnajyoti Mukherjee 2019-11-20

Dear all,

I have one column matrix with N array, and I want to check whether any two elements are equal or not? And if two or more numbers are equal, how to find their position on the array? How can I do that by coding?

Thanks

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Answer 1

Guillaume 2019-11-19

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https://ww2.mathworks.cn/matlabcentral/answers/491935-how-to-check-whether-any-two-elements-are-equal-or-not-in-a-nx1-array-in-matlab#answer_402301

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x = [1 2 3 4 2 5 6 3 7 8 9 10];  %demo data. Works with column or row vectors
[loc1, loc2] = find(tril(x == x.', -1));  %location of duplicates
dupvalues = x(loc1);  %same as x(loc2) obviously
table(dupvalues(:), loc1, loc2, 'VariableNames', {'DuplicateValue', 'FirstIndex', 'SecondIndex'}) %for pretty display

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Swarnajyoti Mukherjee 2019-11-20

It is working perfectly, thanks.

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Answer 2

Vladimir Sovkov 2019-11-19

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https://ww2.mathworks.cn/matlabcentral/answers/491935-how-to-check-whether-any-two-elements-are-equal-or-not-in-a-nx1-array-in-matlab#answer_402299

在 MATLAB Online 中打开

%%    
z=randi(5,10,1); % forms a sample array; replace it with an array of your interest
%%
[~,indx]=sort(z);
k0=1;
while k0<=numel(z)
    if k0<numel(z)
        k1=find(z(indx(k0+1:end))>z(indx(k0)),1); % if you do not need the exact coincidence but a tolerant closeness, change it to "k1=find(z(indx(k0+1:end))-z(indx(k0))>epss,1)" with the epss being the satisfying tolerance
    else
        k1=[];
    end
    if isempty(k1)
        k1=numel(z);
    else
        k1=k1+k0-1;
    end
    disp(strcat('for z=',num2str(z(indx(k0)))));
    disp(sort(indx(k0:k1))');
    k0=k1+1;
end