How do I select some data from a matrix?

I have for example this matrix

A=[2 0.9;
   2 0.8;
   2 1.0;
   2 0.8;
   3 0.3; 
   3 0.7; 
   3 0.8;
   3 0.7]

I want to have just the first two rows of A in each repetition. The "repetition" is in column 1 of A. Here, the repetition is 2 and 3. So B equals:

B=[2 0.9;
   2 0.8;
   3 0.3;
   3 0.7]

Thanks for help.

[Azzi Abdelmalek]

this is not clear, what kind of repetition? only in in first column?

[Rita]

Sorry about that.

I mean column 1 = [2 2 2 3 3 3 3] are repetitions. In my real matrix I have 500 times of data from 2 to 20 and I want to create an matrix with the first 100 times of 2 ,3,4,...20 for the first column and the corresponding values for each row.

I am looking for a function which can make B like this:

B=[A(1:2,:);A(5:7,:)]

I need to extend this for my real data.

Thanks

Answer 1

[Azzi Abdelmalek]

[~,ii]=unique(A(:,1),'stable');
jj=sort([ii,ii+1]);
out=A(jj,:)

[Rita]

Thanks Azzi