Average of the Vector elements in the matrix

I have a matrix of 815*440 and I need to take the average of every 20 elements in all the rows and find the output as 815*22

Any help is appreciated

Thanks

[Kirby Fears]

Trying to understand your questions: are you trying to compute the mean of columns 1, 21, 41,..., 421 for each row, then repeat this exercise for columns 2, 22, ... , 422, and keep repeating until you have a 815 x 22 matrix of such means? This would actually give an 815 x 20 matrix...

Are you instead trying to take the average of columns 1,2,...,20 for each row, and repeat for columns 21,22,...,40, etc until you get to the mean of columns 421,422,...,440? This would give an 815 x 22 output as you mentioned.

[Jab]

I am trying to do your second option

[Kirby Fears]

The answer I posted below solves that problem. Please give it a try.

Answer 1

[Kirby Fears]

Below is a loop to take the mean of the first 20 columns, then the next 20 columns, etc. Let me know if this is not the computation you were trying to perform.

% Creating dummy matrix for example solution
a=reshape(1:815*440,815,440);

% Width of column groupings
colgroup=20;

% Initialize mean results array
results=NaN(size(a,1),size(a,2)/colgroup);

% Take means in loop
for iter=1:size(results,2),
    startcol=colgroup*(iter-1)+1;
    results(:,iter)=mean(a(:,startcol:startcol+colgroup-1),2);
end,

Answer 2

[James Tursa]

Assuming you are averaging every 20 elements, not a sliding window:

A = your 815 x 440 matrix
m = mean(reshape(A',20,[]));
Anew = reshape(m,22,[])';