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sum and average of a vector

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shalipse
shalipse 2016-7-30
回答： Image Analyst 2016-7-30
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
  2 个评论
John D'Errico
John D'Errico 2016-7-30
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.

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2016-7-30
编辑：Azzi Abdelmalek 2016-7-30
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,[]))
  2 个评论
shalipse
shalipse 2016-7-30
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
shalipse 2016-7-30
Many thanks. I appreciate your time

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更多回答（2 个）

Andrei Bobrov
Andrei Bobrov 2016-7-30
z = accumarray(ceil((1:numel(A))'/3),A(:),[],@mean);
Image Analyst
Image Analyst 2016-7-30
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.

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