Data filtering(Cut from half length of index until next index )

I have this kind of data. First column and seconds column refer to an index and x value relatively.

data = [1 200; 1 201; 1 202; 1 201; 2 301; 2 313; 2 311; 3 401; 3 452; 3 433; 3 405; 4 504; 4 303; 4 604; 4 703; 5 600; 5 700; 5 606; 5 703; 5 905; 5 444;];

For example, I want to get rid of half rows of each index.

I'd like to have this kind of data that has half length (or tird whatever ratio) of index.

data = [1 200; 1 201;  2 301; 2 313; 3 401; 3 452; 4 604 4 703; 5 600; 5 700; 5 606;];

for i = max(data(:,1));
TF = sum(data(:,1)==i)+sum(data(:,1)==i-1);
%TF2 = sum(data(:,1)==i-1);
data(TF./2+1:TF,:) = [];
end %My code doesn't work at all:(

If anyone can help, it would be greatly appreciated.

Thank you!

Answer 1

[Andrei Bobrov]

data2 = data(cell2mat(accumarray(data(:,1),...
    (1:size(data,1))',[],@(x){x(1:ceil(numel(x)/2))})),:);

[Jaehwi Bong]

Thank you for your answer!