Delete unique element in column

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Mate 2u
Mate 2u 2012-6-29
编辑： Miguel L 2015-12-27
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.
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Jan
Jan 2012-6-29
编辑：Jan 2012-6-29
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 2015-12-27
编辑：Miguel L 2015-12-27
¡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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Jan
Jan 2012-6-29
What about:
unique(x, 'rows')
?

更多回答（1 个）

Ryan
Ryan 2012-6-29
编辑：Ryan 2012-6-29
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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