Check if any elements of cell array are equal ?

Question

Hirak Basumatary 2019-6-13

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https://ww2.mathworks.cn/matlabcentral/answers/466954-check-if-any-elements-of-cell-array-are-equal

评论： VK Bhardwaj 2019-6-14

Suppose if I have cell array a{1}=[1 1 0]; a{2}=[0 0 0]; a{3}=[0 0 0]. I want to check if any elements of the cell array are equal. If i use " isequal(a{:}) " then it returns "Logical 0". However, we can see that a{2} == a{3}. So, i need the answer to be "Logical 1" as some of the elements of the cell array are equal. Is there any built-in function to check that directly in MATLAB.

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KALYAN ACHARJYA 2019-6-13

编辑：KALYAN ACHARJYA 2019-6-13

Yes, but it can be done using multiple steps, not in single function.

Hirak Basumatary 2019-6-13

Can you suggest me an algo?

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Answer 1

Stephen23 2019-6-14

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https://ww2.mathworks.cn/matlabcentral/answers/466954-check-if-any-elements-of-cell-array-are-equal#answer_379143

编辑：Stephen23 2019-6-14

在 MATLAB Online 中打开

Matching:

>> a{1}=[1,1,0];
>> a{2}=[9,9,9,9];
>> a{3}=[1,1,0];
>> a{4}=[];
>> N = numel(a);
>> [X,Y] = ndgrid(1:N);
>> Z = tril(true(N),-1);
>> any(arrayfun(@(x,y)isequal(a{x},a{y}),X(Z),Y(Z)))
ans = 1

vs. non-matching:

>> a{1}=[1,1,1];
>> any(arrayfun(@(x,y)isequal(a{x},a{y}),X(Z),Y(Z)))
ans = 0

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Stephen23 2019-6-14

编辑：Stephen23 2019-6-14

@madhan ravi: thank you :)

Hirak Basumatary 2019-6-14

@stephen cobeldick: thank you very much. Wil remember this technique for my future problems.

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Answer 2

madhan ravi 2019-6-13

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https://ww2.mathworks.cn/matlabcentral/answers/466954-check-if-any-elements-of-cell-array-are-equal#answer_379062

编辑：madhan ravi 2019-6-14

在 MATLAB Online 中打开

This method works for cells with contents of any sizes:

a{1}=[1 1 0]; % example array
a{2}=[0 10];
a{3}=[1 1 0];
Result = false;
for k = 1:numel(a)
    for l = 1:numel(a)
    if k~=l
    if isequal(a{k},a{l})
       Result = true;
       break
    end
    end
end
end

Note: The below two methods assume each cell has the same number of elements.

a{1}=[1 1 0]; 
a{2}=[0 0 0]; 
a{3}=[0 0 0];
A = vertcat(a{:});
Result = false;
for k = 1:numel(a)
  if nnz(ismember(A,a{k},'rows'))>1
      Result = true;
      break
  end
end
% or
idx=all(A'==permute(reshape(A,[],1,size(A,1)),[3,2,1]));
Result=any(squeeze(sum(idx,2))>1)

Choose which method you like the best , some mould can be given to the above but I’m off for the day perhaps will look into it tomorrow.

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Stephen23 2019-6-14

编辑：Stephen23 2019-6-14

在 MATLAB Online 中打开

+1 the nested loops (first algorithm) is probably the most efficient approach to this. Note that break only exits the inner loop while the outer loop keeps running (but this does not affect the result). An improvement to avoid testing pairs of arrays twice is to use the outer-loop's iteration variable to set the range of the inner loop (here the short-circuit || makes the code quite efficient without break), e.g.:

>> a{1}=[1,1,0];
>> a{2}=[9,9,9,9];
>> a{3}=[1,1,0];
>> a{4}=[];
>> N=numel(a);
>> Z=false;
>> for x=1:N, for y=x+1:N, Z=Z||isequal(a{x},a{y}); end, end
>> Z
Z = 1

madhan ravi 2019-6-14

@Stephen Cobeldick: Thank you very much!

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Answer 3

VK Bhardwaj 2019-6-13

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https://ww2.mathworks.cn/matlabcentral/answers/466954-check-if-any-elements-of-cell-array-are-equal#answer_379068

编辑：VK Bhardwaj 2019-6-14

在 MATLAB Online 中打开

function y = checkequal(x)
% Input 'x' should be cell array
% Output 'y' logical value true. If any input cell array index is equal to
% another else false
% Example1:
% a{1}=[1 1 0]; a{2}=[0 0 0]; a{3}=[0 0 0];
% y = checkequal(a);
% Output is y = logical(1)
% Example2:
% a{1}=[1 1 0]; a{2}=[0 1 0]; a{3}=[0 0 0];
% y = checkequal(a);
% Output is y = logical(0)
y = false;
num = numel(x);
for i = 1:num
    for j = 1:num
        if i~=j
            if isequal(x{i},x{j})
                y = true;
                return;
            end
        end
    end
end
end