Generating a long vector from two other vectors

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    ...

Answer 1

[Azzi Abdelmalek]

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

[Shoaibur Rahman]

Thanks a lot. It works. I read the docs of functions you have used, but was not clear about how it is working. Could you please explain the the command in brief ( out=cell2mat(arrayfun(@(x,y) repmat(x,1,y),a,b,'un',0)) )?

Answer 2

[Steven Lord]

 v = repelem([20 13 24], [3 2 4])