sum and average of a vector

Dear all,

I am fairly new to matlab and struggling to write a code. I will be grateful to be given a push. For instance given a vector one to hundered, I want to take every three values and average them. Also print the output result. E.g

(1+2+3)/3 + (4+5+6)/3 + (7+8+9)/3 + .......

Thank you in advance and I appreciate your contribution.

regards

Ismaeel

[John D'Errico]

Unless your vector has a length that is a multiple of 3, any such solution will fail. So 100 elements will not allow you to do that.

The simple solution uses reshape and sum to solve the problem. So why not try it? You will learn by trying. So see what reshape does. How might that help you? Then think about what the sum function does.

[shalipse]

Many thanks John.

Answer 1

[Azzi Abdelmalek]

A=randi(10,30,1)  % Example
mean(reshape(A,3,[]))

If the length of A is not a multiple of 3

A=randi(10,38,1)
n=numel(A)
p=mod(-n,3)
A(n+1:n+p)=nan  % complete with nan
out=nanmean(reshape(A,3,[]))

[shalipse]

Many thanks Azzi, that was quick... Is it possible to use a loop command with a conditional statement that would stop the computation at 99, given that no values can be added to the iteration after this.

Thank you again

[shalipse]

Many thanks. I appreciate your time

Answer 2

[Andrei Bobrov]

z = accumarray(ceil((1:numel(A))'/3),A(:),[],@mean);

Answer 3

[Image Analyst]

Yet another way using conv() to take the moving average:

m = 1 : 33 % Create sample data.
m2 = conv(m, [1,1,1]/3, 'valid');  % Intermediate array.
output = m2(1:3:end) % Subsample to get final array.