Delete unique element in column

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.

[Jan]

Just for clarification:

a = [1,2; 1,3; 3,4] => [3,4] ?

[Jan]

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]

¡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.

Answer 1

[Jan]

What about:

unique(x, 'rows')

?

[Ryan]

A = [1 2; 1 3; 3 4];
unique(A,'rows')
ans = 
      1 2
      1 3
      2 4

Answer 2

[Ryan]

Based off of Jan's answer:

A = [1 2; 1 3; 3 4];
[B, I, J] = unique(A(:,1),'last');
NewMatrix = A(I,:);