Using for loops in order to find average of matrix

Hi I have a 1000x100000 matrix.

I'd like to know the average of the numbers in each column, so that's 100000 values I'm looking for.

I can use the mean() command, and I'm trying to get this done using for loop and preallocation. What i have atm:

mu = 2;
SD = 3;
m = 1000;
n = 100000;
random_matrix = randn(m,n)*SD + mu;

a=zeros(1,n);
for k=1:m
    for h=1:n
        a(k,h) = means(random_matrix(k,h));
    end
end

I dont know whats wrong arrgh. Can someone help me? I think i am not wrong at all, but my program does not stop running...

Thanks in advance!

Answer 1

[Bob Thompson]

You can use mean to average all values in a certain direction.

mu = 2;
SD = 3;
m = 1000;
n = 100000;
random_matrix = randn(m,n)*SD + mu;
a=mean(random_matrix,1);

[Catayoun Lissa Eleonore Azarm]

ok, thank you! The thing is, i want to use a loop. Do you know how i get these values using a loop?

[Bob Thompson]

You can do the same operation by indexing for the entire column, rather than specific individual values.

a = zeros(1,n);
for i = 1:n
    a(i) = mean(random_matrix(:,i));
end

[Catayoun Lissa Eleonore Azarm]

Thank you very much! that helped me a lot!

[Catayoun Lissa Eleonore Azarm]

It worked for every case exept this one:

zscored1=zeros(m,n);
tic;
for i = 1:n
    zscored1(i) = (random_matrix(:,i) - means1) ./ SDs1;
end
x(3)=toc;

It says "Unable to perform assignment because the left and right sides have a different number of elements." Do you know whats wrong?

[Bob Thompson]

It means that the size of random_matrix(:,i), means1, and SDs1 don't agree. Either means1 and SDs1 need to be single elements or they need to be the same size as random_matrix(:,i).