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Delete unique element in column

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Mate 2u
Mate 2u am 29 Jun. 2012
Bearbeitet: Miguel L am 27 Dez. 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 Kommentare
Jan
Jan am 29 Jun. 2012
Bearbeitet: Jan am 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 am 27 Dez. 2015
Bearbeitet: Miguel L am 27 Dez. 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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Akzeptierte Antwort

Jan
Jan am 29 Jun. 2012
What about:
unique(x, 'rows')
?
  1 Kommentar
Ryan
Ryan am 29 Jun. 2012
A = [1 2; 1 3; 3 4];
unique(A,'rows')
ans =
1 2
1 3
2 4

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Ryan
Ryan am 29 Jun. 2012
Bearbeitet: Ryan am 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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