For an nx3 matrix, order the 3 entries in each row, then order rows from least to greatest, then check for repeated rows.

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Rebecca 2012-6-20

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I have a matrix that is nx3, and am trying to do the following with it: 1) For each row, sort its three entries from smallest to largest. 2) Order the rows from smallest to greatest by the first entry (using the sortrows function). 3) Check for repeated rows in the matrix. If the row of three numbers appears more than once, I would like to delete all of its appearances from the matrix. In the end, the output should be a matrix containing all rows that only appeared once in the original.

Any help would be appreciated with this. Thank you!

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Answer 1

Nirmal 2012-6-20

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This should do the job for you.

a=rand(5,3);
[m,n]=size(a);
a=sort(a,2);
a=sortrows(a,3);
temp=[];
for i=1:m
    flag=0;
    for j=1:m
        if i==j
            continue;
        end
        if sum(a(i,:)==a(j,:))==3
            flag=1;
            break;
        end
    end
      if flag==0
          temp=[temp;a(i,:)];
      end
end
a=temp;

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Answer 2

Sean de Wolski 2012-6-20

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In R2012a or later, this will do it:

X = [[1 3 2;1 3 2]; rand(10,3)];
[Y,~,idx] = unique(sortrows(sort(X,2,'ascend'),1:3),'rows','stable');
idx2keep= accumarray(idx,1)<=1;
Y = Y(idx2keep,:);