How to sum multiple rows elements within the matrix

I have a matrix with (30*70 ).

Does anybody know how I can calculate the the average of every 3 rows together?

for example : rows from (1-3) to be 1 row and second row to be the average of (4-6) and so on .

the final matrix must be 10*70

Answer 1

[Sriram Tadavarty]

Hi Abdulhakim,

The mean and reshape functions are helpful for your case. Here is the code that does what is asked for.

% Consider the input matrix is a
a = rand(30,70);

% Reshape the matrix such a way you have only 3 rows
aReshape = reshape(a,3,[]); % This turns up to 3 x 700

% Use the mean function
avg = mean(aReshape); % This returns the average of 3 elements in each column (1 x 700)

% Now to get the desired ouput in matrix form, perform the reshape again
out = reshape(avg,[],70); % Output size is (10 x 70)

The links to the document page of mean and reshape functions are:

https://www.mathworks.com/help/matlab/ref/mean.html

https://www.mathworks.com/help/matlab/ref/reshape.html

Hope this helps.

Regards,

Sriram

[Abdulhakim Alezzi]

Dear Sriram , That is very helpfull, it workd perfectly.

Answer 2

[Fangjun Jiang]

a=rand(6,7);
b=reshape(a,3,[]);
c=mean(b);
d=reshape(c,2,[]);

[Abdulhakim Alezzi]

Dear Fangjun,

Thank you very much. the concept is very correct, but the output was a matrix of 2x150.