find mean for each 4 row in 124x7 matrix

Hi all ,,,

I have matrix U=124 x 7

I want to find the mean through all 4 rows of each column

the result be 31 x7

Answer 1

[madhan ravi]

b=mat2cell(U,repmat(4,1,size(U,1)/4)); % where U is 124 X 7 matrix
R=cellfun(@(x) mean(x),b,'un',0);
Result=vertcat(R{:})

[nada]

Thank you alot ..it is work

if there is a simple loop to do that..

[madhan ravi]

"if there is a simple loop to do that.."

[m,n]=size(U);
Result=zeros(m/4,n);
for k = 1:m/4
   Result(k,:)=mean(U(k*4-3:k*4,:));
end

[nada]

That's wonderful ......thank you again

Answer 2

[Image Analyst]

You can do it in as little as two lines of code with blockproc() from the Image Processign Toolbox:

U = randi(9, 124, 7); % Original sample data

% Define the function that we will apply to each block.
% This function will return a value that is the mean of the elements in the block.
% Output array will be 31 by 7.
meanFilterFunction = @(theBlockStructure) mean(theBlockStructure.data(:));

% Block process the image to replace every pixel in the 
% 4 pixel by 1 pixel block by the mean of the pixels in the block.
blockSize = [4 1];
blockMeanArray = blockproc(U, blockSize, meanFilterFunction); % Works.

blockproc() moves along in "jumps" of the block size that you specify - it does not slide over by one element at a time like conv2() does. If you'd used conv2() you would have to subsample the result.

[nada]

Thank you

but the result was not the elements mean

[Image Analyst]

It most certainly was. I just double checked it. Check your numbers again.