index info for CAT

I am concatenating vectors x1,x2,x3 using y=cat(2,x1,x2,x3). Each one of these vectors have different lengths. I need to keep track index information for each one of them. How can I do this without loops.

x1=[1 1 0 1]; x2=[1 0]; x3=[1 1 1];

         y=cat(2,x1,x2,x3);
          = [1 1 0 1 1 0 1 1 1]

    index = [1  4;5 6;7 9]

Answer 1

[Azzi Abdelmalek]

index=reshape(cumsum([1 numel(x1)-1 1 numel(x2)-1 1 numel(x3)-1]),2,[])'

[Azzi Abdelmalek]

Instead of using 3 variables x1,x2 and x3 you can use a single variable

x={[1 1 0 1];[1 0];[1 1 1]}  % x is a cell array
you can get your three variables
x{1}
x{2}
x{3}

% Now you can get y
y=cell2mat(x')

out=reshape(cumsum([1 numel(x1)-1 1 numel(x2)-1 1 numel(x3)-1]),2,[])'