MATLAB: Efficient way of transforming vector

Question

Hi,

I have a rather simple question on vector manipulation. I want to do some matrix manipulation as efficiently as possible and I think I found a solution, but therefore I have to do some vector manipulation. For example, I want to transform vector A into vector B:

A =

     2
     1
     0
     3

B =

     1
     1
     2
     4
     4
     4

So each element of A shows how many times the number 1,2,3,4… should be repeated. Is there a way to do this transformation in an efficient way without setting up a loop myself?

Thanks for your answer!

Answer 1

A =[2
     1
     0
     3];
n = A ~= 0;
k = cumsum(A);
k1 = k(n);
s = (1:numel(A))';
s1 = s(n);
k2 = k1 - A(n) + 1;
ii = zeros(k(end),1);
ii(k2) = 1;
idx = cumsum(ii);
out = s1(idx)