Mean of matrix by columns

Hello! I'm looking for a function to get the mean of two (or more) columns:

 A = 1     2     3
     4     5     6
     7     8     9

 f(A) = 
    1.5000    2.5000
    4.5000    5.5000
    7.5000    8.5000

How can I do that in a simple way, for a generic matrix? Thank you.

Answer 1

[Andrei Bobrov]

conv2(A,[.5 .5],'valid')

[Alessandro Masullo]

Thank you!!

Answer 2

[sixwwwwww]

Dear Alessandro, you can use MATLAB function "mean" for this purpose. Here is description: http://www.mathworks.com/help/matlab/ref/mean.html. In Your case just use

mean(A)

[Alessandro Masullo]

I don't think this is the function I need... mean(A) will do the mean of each column, but what I want is the mean of all the column 2 by 2. I do this in this way, but it is not so good:

     for k = 1:3
        avgA(:,k) = (A(:,k) + A(:,k+1))/2;
     end

[sixwwwwww]

You need mean of two consecutive elements in a row? For example,

A = [1 2 3 4]

You need

meanA = [1.5 2.5 3.5]

Is it what you need?

[Alessandro Masullo]

Yes, but the same thing for all the column of a matrix:

 A = 1  <->   2  <->   3
     4  <->   5  <->   6
     7  <->   8  <->   9
 f(A) = 
    1.5000    2.5000
    4.5000    5.5000
    7.5000    8.5000

[sixwwwwww]

Here is an example code for this:

A = rand(3);
[m, n] = size(A);
for i = 1:m
    for j = 1:n - 1
        A_avg(i, j) = (A(i, j) + A(i, j + 1))/2;
    end
end
disp(A)
disp(A_avg)

Is it ok?

[Alessandro Masullo]

Yes, this is what I'm trying to do :D I don't want to bug you, but I'm trying to do this with matrix indexing, because I already do this with a loop, but I have very big matrix and the same operation to be done on different matrix of different sizes...

[sixwwwwww]

I think in anyway you will need to use at least one for loop. However if I will have better idea then I will come back to it

Answer 3

[Jan]

B = (A(1:end-1) + A(2:end)) * 0.5