How to calculate average of certain value in a matrix?

Hello, My problem is about how to calculate the average of certain values in a large matrix. I know how to calculate the 1st average of the matrix with matlab, but for the other one I tried with a for loop but I didn't manage to solve the problem.

Example:

calculate the average of every 2 values of A

A=

1

2

3

4

5

6

7

8

Av1=1,5 WITH MATLAB Av1=sum(A(1:2;1),1)./2

Av2=3,5

Av3=5,5

Av4=7,5

I did the following loop but it doesn't work :

for i=1:3

for k=2:4

Av=sum(A(i*2+1:2*k,1),1)./2

end

end

Thank you in advance

Answer 1

[Andrei Bobrov]

Av = mean(A([1:2:end;2:2:end]));

or

Av = sum(A([1:2:end;2:2:end]))/2;

ADD

 n = 3;
 Av = accumarray(floor((n:numel(A)+n-1)/n)',A(:),[],@mean);

or

n=3;
p = reshape([A(:);nan(mod(-numel(A),n),1)],n,[]);
l = isnan(p);
p(l) = 0;
Av = sum(p)./sum(~l);

if rem(numel(A),n) == 0 , just:

Av = mean(reshape(A,n,[]));

if you have Image Processing Toolbox then

Av = blockproc(A,[1 n],@(x)mean(x.data));

[afrya]

thank you for your answer ,it works well.Now,how can i do it to calculate for example every 3 values of the matrix?

[afrya]

I didn't understand the syntax

[Andrei Bobrov]

see ADD part

Answer 2

[Omair]

Do you mean every 2nd value of A?

mean(A(1:2:end))

[afrya]

I mean,how to calculate every 2 values of A At the end, you'll get 4 averages in the case of the exemple