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
Rebecca on 20 Jun 2012
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!

Answers (2)

Nirmal
Nirmal on 20 Jun 2012
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;

Sean de Wolski
Sean de Wolski on 20 Jun 2012
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,:);

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