Find element in matrix

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Eduardo
Eduardo on 3 Apr 2012
Hello, I have a matrice and i whant to find if there are 2 iqual elements in diferent rows...
A =
1 2
3 5
2 4
6 1
In this case i should find the number 1 and 2. But i whant to find one at a time. Can someone help me with this? Thank´s.
  1 Comment
Image Analyst
Image Analyst on 6 Apr 2012
A is comprised on ONLY integers, right? Else you need to consider the FAQ: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

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Accepted Answer

Richard Brown
Richard Brown on 11 Apr 2012
Here's a slightly uglier way that will work. If you need the code to perform quickly, you'd obviously preallocate your arrays m and z
z = zeros(0, 2);
m = [];
for a = unique(A(:)');
[I, ~] = find(A == a);
if numel(I) == 2
m = [m a];
z = [z; setdiff(reshape(A(I, :), 1, 4), a)];
end
end

More Answers (3)

Thomas
Thomas on 3 Apr 2012
A = [1 2
3 5
2 4
6 1 ];
intersect(A(:,1),A(:,2))

Thomas
Thomas on 6 Apr 2012
Try this
clear all
A = [1 2
3 5
2 4
6 1 ];
c=intersect(A(:,1),A(:,2));
for i=1:length(c)
[p(:,:),q(:,:)]=find(A==c(i));
l=A(p(:),:);
m=unique(l)';
z(i,:)=m(m~=c(i));
end
c % common elements 1 and 2
z % elements associated with 1=2,6 and 2=1,4
Output will be
c =
1.00
2.00
z =
2.00 6.00
1.00 4.00
  1 Comment
Eduardo
Eduardo on 11 Apr 2012
First of all, thanks.
It works only in some cases... In the case of the same element be on the same row but diferent lines, with this code can´t be found... Any idea?

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Eduardo
Eduardo on 6 Apr 2012
Thank´s... What i need is something more complex, but i didn´t explain it... If i find 2 iqual elements like number 1, for example, what i need to do is connect the other elements in the same line. If i find 1 in to lines ([1 2] and [6 1]) what i need to do is create a new line with [2 6]. I don´t know how to do it...

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