MATLAB: Generating a long vector from two other vectors

vectorization

I got stuck with a (may be) simple problem. Here are two vectors, like:
a = [20 13 24 ...];
b = [3 2 4 ...];
How can I create a new vector that contains 3 20s, 2 13s, 4 24s, and so on? (Not using any loop). The output will look like as shown in c:
c =
   20    20    20    13    13    24    24    24    24    ...

Best Answer

a = [20 13 24 ];
b = [3 2 4 ];
out=cell2mat(arrayfun(@(x,y) repmat(x,1,y),a,b,'un',0))
or with a for loop
a = [20 13 24 ];
b = [3 2 4 ];
out=zeros(1,numel(a))
c=[ 0 cumsum(b)]
for k=1:numel(a)
  out(c(k)+1:c(k+1))=a(k)*ones(1,b(k))
end
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