How to decimate the matrix

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kubyk
kubyk 2014-6-13
编辑： Matthew 2015-3-6
Hi, I have matrix of data and I would like to decimate the data with command "decimate(x,r)". The matrix has 100 rows. I tried to get it with FOR loop for decimation each row but still wrong. I just get the first decimated row. Here is my code
data %matrix of data
r=10; %decimation factor
% n=100; %number of rows
for i=1:size(data,1)
x=data(i,:);
y=decimate(x,r);
end
Thanks

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Image Analyst
Image Analyst 2014-6-13
How about
outputMatrix = data(1:10:end, :);
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kubyk
kubyk 2014-6-13
of course, I am stupid... thanks a lot
Even so, later I would like to process row by row. Each row give me some information about EEG response. Question is how to do the loop which will go through the matrix row by row.
Matthew
Matthew 2015-3-6
编辑：Matthew 2015-3-6
The decimate function doesn't simply remove data points. It actually low-pass filters the data before downsampling. So decimate(x, r) and x(1:r:end) don't return the same results.
If you actually want to use the decimate function, as far as I can tell you have to use a for loop. I came across this question when I was trying to solve this same problem.
To address the OP's question, in your code, every loop iteration overwrites the value of y. I think the correct way to do it is something like:
y = zeros( size(data,1), ceil(size(data,2)/r) );
for i = 1:size(data,1)
x = data(i, :);
y(i, :) = decimate(x,r); % <<< this was the mistake
end

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