# Using for loops in order to find average of matrix

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Commentato: Bob Thompson il 1 Feb 2021
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...
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### Risposta accettata

Bob Thompson il 1 Feb 2021
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);
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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 il 1 Feb 2021
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).

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