Asked by Hirak Basumatary
on 13 Jun 2019

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.

Answer by Stephen Cobeldick
on 14 Jun 2019

Edited by Stephen Cobeldick
on 14 Jun 2019

Accepted Answer

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

madhan ravi
on 14 Jun 2019

+1, dope solution!

Stephen Cobeldick
on 14 Jun 2019

Hirak Basumatary
on 14 Jun 2019

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

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Answer by madhan ravi
on 13 Jun 2019

Edited by madhan ravi
on 14 Jun 2019

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.

KALYAN ACHARJYA
on 13 Jun 2019

+1

Stephen Cobeldick
on 14 Jun 2019

+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
on 14 Jun 2019

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Answer by VK Bhardwaj
on 13 Jun 2019

Edited by VK Bhardwaj
on 14 Jun 2019

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

madhan ravi
on 14 Jun 2019

Hirak Basumatary
on 14 Jun 2019

@madhan ravi: thank you very much. Didn't spot this.

VK Bhardwaj
on 14 Jun 2019

@madhan ravi: Thanks for spotting the issue. I have updated the code.

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## 2 Comments

## KALYAN ACHARJYA (view profile)

Direct link to this comment:https://in.mathworks.com/matlabcentral/answers/466954-check-if-any-elements-of-cell-array-are-equal#comment_714455

## Hirak Basumatary (view profile)

Direct link to this comment:https://in.mathworks.com/matlabcentral/answers/466954-check-if-any-elements-of-cell-array-are-equal#comment_714456

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