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Delete unique element in column

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Mate 2u
Mate 2u on 29 Jun 2012
Edited: Miguel L on 27 Dec 2015
Hi I have a 25,000,000x2 matrix. I want to delete all Rows which have the same elements in column 1. So I would require only unique elements in column 1 and their corresponding values in column 2.

  3 Comments

Jan
Jan on 29 Jun 2012
Just for clarification:
a = [1,2; 1,3; 3,4] => [3,4] ?
Jan
Jan on 29 Jun 2012
Mate 2u has written as comment to my wrong answer:
Hi Jan for [1,2; 1,3; 3,4] we would expect to see => [1,3; 3,4] as 1 occured more than once (take the last of the non unique values).
This means, that he does not "want to delete all Rows which have the same elements in column 1".
Miguel L
Miguel L on 27 Dec 2015
¡Hello Jan!
Regarding to this question, actually I wanna get "a = [1,2; 1,3; 3,4] => [3,4] ", as you suggest at first ¿Could you help me? Tank you in advance.

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Accepted Answer

Jan
Jan on 29 Jun 2012
What about:
unique(x, 'rows')
?

  1 Comment

Ryan
Ryan on 29 Jun 2012
A = [1 2; 1 3; 3 4];
unique(A,'rows')
ans =
1 2
1 3
2 4

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More Answers (1)

Ryan
Ryan on 29 Jun 2012
Edited: Ryan on 29 Jun 2012
Based off of Jan's answer:
A = [1 2; 1 3; 3 4];
[B, I, J] = unique(A(:,1),'last');
NewMatrix = A(I,:);

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