how to repeat elements of column vector

I have a matrix of 40500*4 and which its first column is time stamp of 1 to 1500 (for example 300 rows have the value 1 for its time 500 rows have the value 2 and ..... I have another column vector which is 1500*1. what I want to do is to extend the size my column vector to 40500*1 (the same size with my matrix rows) in the way when the time value is 1 repeat the first element of my column vector for n times where the n is the number of rows in my matrix which have the value 1 in the time column. I wrote a code something like that but it takes ages to run. could you please help me to write a better code. Thanks

data = 40500*1
data2 =1500*1;
  n=max(data=(:,1));  %%n=1500
  m = size(data,1); %%%m=40500  
  x = cell(n,1)
  for i =1:n
    x{i}=find(dataCopy(:,1)==i); %%%x = 1500
  end
newdata = cell(m,1);
  for i=1:n
    for j = 1:m
     newdata{j}=repelem(data2(i),numel(x{i,1}));
   end
  end

Answer 1

[Ben Frankel]

You can get a vector where V(i) = count of timestamp i, with:

V = diff([0; find(diff([data(:, 1); 1]))])

Then you can stretch your column vector C with:

stretched = repelem(C, V, 1);

[Sara]

Thanks a lot. your code is perfect.