Check if any elements of cell array are equal ?

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.

[KALYAN ACHARJYA]

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

[Hirak Basumatary]

Can you suggest me an algo?

Answer 1

[Stephen23]

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]

+1, dope solution!

[Stephen23]

@madhan ravi: thank you :)

[Hirak Basumatary]

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

Answer 2

[madhan ravi]

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]

+1

[Stephen23]

+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]

@Stephen Cobeldick: Thank you very much!

Answer 3

[VK Bhardwaj]

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]

@Hirak: This method only checks the consecutive cells. Note that this method fails for the example:

a{1}=[1 1 0]; 
a{2}=[0 10 0]; 
a{3}=[1 1 0];
y = checkequal(a) 

Gives:

y =

  logical

   0

[Stephen23]

@madhan ravi: well spotted!

[madhan ravi]

@Stephen Cobeldick: Thank you!

[Hirak Basumatary]

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

[VK Bhardwaj]

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