Calculating sum of array elements and reiterate for entire array in MATLAB

Question

I have a vector A of size 7812x1 and would like to calculate the sum of fixed windows of length 21 (so 372 blocks). This should be reiterated, so that the output should return a vector of size 372x1.

I have t=7812, p=372, w=21;

for t=1:p
   out = sum(A((t*w-w+1):(t*w)));
end

This code, however, does not work. My idea is that the part ((t*w-w+1):(t*w)) allows for something like a rolling window. The window is of length 21, so there is not really a need to express is with variables, yet I think it keeps some flexibility.

I've seen potentially related questions (such a partial sum of a vector), yet I'm not sure whether this would result the output desired.

Luis Mendo · Accepted Answer · 2017-11-06 12:15:11Z

3

Reshape into a matrix so that each block of A is a column, and compute the sum of each colum:

result = sum(reshape(A, w, []), 1);

edited Nov 6, 2017 at 12:15

answered Nov 6, 2017 at 11:26

Luis Mendo

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2 Comments

Joe Over a year ago

I guess in my case it should be the sum instead of the mean, in order to obtain the same results as @Leander Moesinger. Otherwise, I'm taking the mean of each block, right?. However, the solution is intuitive and works perfectly well. Many thanks!

Luis Mendo Over a year ago

@Joe Yes, sum instead of mean, sorry. Corrected

Leander Moesinger · Accepted Answer · 2017-11-06 11:36:48Z

1

Following your idea of using a rolling/moving window (requires Matlab 2016a or later):

t = 7812; w = 21; % your parameters
A = rand(t,1); % generate some test data

B = movsum(A,w); % the sum of a moving window with width w
out = B(ceil(w/2):w:end); % get every w'th element

edited Nov 6, 2017 at 11:36

answered Nov 6, 2017 at 11:30

Leander Moesinger

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