MATLAB: How to group double matrix based on the first column values and list second values as observations

groupobservationsplotstandard error

I have a matrix of double numbers:
X = 
1   2.1
1   2.3
2   1.9
3   4.0
1   2.0
I want to group this based on the first column value and list the second values as observations:
Result = [
  1  2.1  2.3  2.0
  2  1.9
  3  4.0
];
How can I achieve this? And is this a good way of representing data if I need to calculate their standard errors and plot both observations and error bars on a plot? Any help will be appreciated! Thanks.

Best Answer

X = [1   2.1
1   2.3
2   1.9
3   4.0
1   2.0]
[id,~,j]=unique(X(:,1));
val = accumarray(j,X(:,2),[],@(x) {x.'});
s = struct('id', num2cell(id), 'val', val);
for k=1:length(s)
    sk = s(k);
    fprintf('id = %d, val = %s, std = %f\n', sk.id, mat2str(sk.val), std(sk.val));
end
Related Question