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arraysmatlabmatrixuniquenon-repetitive

Non-repeated arrays in a matrix in matlab

I am looking for non-repeated rows in a matrix.

Assume:

A =

 8     1
 2     2
 2     2
 2     2
 2     2
 3     6
 5     7
 5     7

I would like to get "B" which is:

B=

 8     1
 3     6

Please mind C=unique(A,'rows') will give us unique rows of "A" which include repeated and non-repeated arrays and only remove repetitious rows. It means:

C =

 2     2
 3     6
 5     7
 8     1

"C" is not the one that I am looking for.

Any help would be greatly appreciated!

Solution

  • Use the second and third outputs of unique as follows:

    [~, ii, jj] = unique(A,'rows');
kk = find(histc(jj,unique(jj))==1);
B = A(sort(ii(kk)),:);

    Or use this more direct bsxfun-based approach:

    B = A(sum(squeeze(all(bsxfun(@eq, A.', permute(A, [2 3 1])))))==1,:);

    These two approaches work in quite generally: A may have any number of columns, and may contain non-integer values.

    If A always has two columns and contains only integer values, you can also do it with accumarray, using the sparse option (sixth input argument) to save memory in case of large values:

    [ii jj] = find(accumarray(A, 1, [], @sum, 0, true)==1);
B = [ii jj];

    Or you can use sparse instead of accumarray:

    [ii jj] = find(sparse(A(:,1),A(:,2),1)==1);
B = [ii jj];