You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: summary_block_means.m
    path of file: ./repos/bspm/thirdparty/spm12/toolbox/marsbar-0.44/@marsy
    
    the code of the file until where you have to start completion: function mus = summary_block_means(Y)
% return raw means over blocks in summary data
% 
% Input
% Y        - marsy object
% 
% mus      - means over block.  Returns B x N matrix
%            where B is number of blocks, and N is number
%            of ROIs 
% 
% $Id$

y = summary_data(Y);
r = block_rows(Y);

B = length(r);
N = size(y, 2);


    
function mus = summary_block_means(Y)
% return raw means over blocks in summary data
% 
% Input
% Y        - marsy object
% 
% mus      - means over block.  Returns B x N matrix
%            where B is number of blocks, and N is number
%            of ROIs 
% 
% $Id$

y = summary_data(Y);
r = block_rows(Y);

B = length(r);
N = size(y, 2);

mus = zeros(B, N);

for b = 1:B
  mus(b, :) = mean(y(r{b},:),1);
end