MATLAB: How would you calculate the average of odd indexed elements of a vector

loops

The code I have to get this answer is mean(V(1:2:end))

but I would I find it using at least one loop?

Best Answer

tot = sum(V(1:2:end));
N = 0;
for idx = 1:2:length(V)
  N = N + 1;
end
tot/N

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MATLAB: Average

data - your array [42x16384]

EDIT

out = mean(reshape(data,size(data,1),[],8),3);

eg:

data - your array [55x72000]

out = mean(reshape(data,size(data,1),[],3),3);

out = squeeze(mean(reshape(data,size(data,1),3,[]),2)) ;

Here is some code that might do the job. I am assuming that your image is truecolor, so the data have dimensions M x N x 3 for some M and N, and the colors are 24-bit, so the data type in R is uint8. If your images are different, you'll have to adjust the code:

n = length(dirlist);
R =  imread([pathname, dirlist(1).name]);
RR = zeros([size(Rav) n]);
% Put the images into an M x N x 3 x 60 array
for m2 = 2:n
  RR(:,:,:,m2) = imread([pathname, dirlist(m2).name]);
end
Rav = mean(RR,4); % average along the 4th dimension of the data
RR = bsxfun(@minus,RR,Rav); % subtract the average from each image

You can examine the kth image with

R = RR(:,:,:,k);
image(R)

Best Answer

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