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How to compare each element of an array with the rest of the elements for several rows independently?

Asked by Mohammad Fazelpour on 13 Apr 2019
Latest activity Commented on by Stephen Cobeldick on 17 Apr 2019
I want to compare each element of an array with the rest of the elements (in a single row of a matrix) and identify which pair(s) of indexes have both values of 1 (in each row). 'nchoosek' works for one row, but when other rows are added like the following example, the code does not work. It is expected the results of each row is independent of other rows.
A =[1 1 0 1 1 0; 0 0 1 0 0 1; 0 0 0 1 1 1; 1 1 1 1 1 1];
for i=1:4
index_matrix(i,:,:) = nchoosek(find(A(i,:)==1),2)
end;

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1 Answer

Answer by Stephen Cobeldick on 13 Apr 2019
 Accepted Answer

Because each array has a different size you will have to use a cell array:
A = [1 1,0,1,1,0;0,0,1,0,0,1;0,0,0,1,1,1;1,1,1,1,1,1];
N = size(A,1);
C = cell(1,N);
for k = 1:N
V = find(A(k,:));
C{k} = nchoosek(V,2);
end
giving:
>> C{:}
ans =
1 2
1 4
1 5
2 4
2 5
4 5
ans =
3 6
ans =
4 5
4 6
5 6
ans =
1 2
1 3
1 4
1 5
1 6
2 3
2 4
2 5
2 6
3 4
3 5
3 6
4 5
4 6
5 6
>>
See also:

  2 Comments

Now, I want to access the cell array, C, and identify how many times different indexes have occurred. For example, in the case of above example, the output would be
Cell Array # of times
1 2 2
1 3 1
1 4 2
......
5 6 2
I wrote this
[row, column] = size(C)
for i=1:4
Sum (i) = cellfun(@(x) find(x=='1 2'), C);
end
which is not correct. Your help is appreciated.
>> M = vertcat(C{:});
>> [U,~,X] = unique(M,'rows');
>> N = histc(X,1:max(X));
>> [U,N]
ans =
1 2 2
1 3 1
1 4 2
1 5 2
1 6 1
2 3 1
2 4 2
2 5 2
2 6 1
3 4 1
3 5 1
3 6 2
4 5 3
4 6 2
5 6 2

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