MATLAB: Choose n out of every 4 elements randomly.

matrix manipulation

I have a 1 by 124 matrix and I want to choose 'n' where n can be 1, 2or 3 from every 4 elements randomly.
This is my code but currently it selects 1 every 4. How can I make it generic, that is it selects 2 or 3 out of 4.
m = length(elements);
  nof4 = m/4;
  randSelect = randi([1 4],1,nof4);
  inds = randSelect+(0:nof4-1)*4;
  output= elements(inds);
Thanks

Best Answer

Try this:
% Create sample data.
m = randi(9, 1, 124);
% Define how many from each block of 4 you want to take
n = 3;
% Reshape m to have 4 columns and 31 rows
mReshaped = reshape(m, [], 4);
[rows, columns] = size(mReshaped);
% Preallocate an output array
out = zeros(rows, n);
for row = 1 : size(mReshaped, 1)
  % Get random column indexes.
  randomColumns = randperm(4, n)
  % Extract those elements into our output matrix.
  out(row,:) = mReshaped(row,randomColumns);
end
out % Print to command window.
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