For loop for applying filter for each column

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Hi I've a signal which I read into matlab as a 4096x28 matrix. I want to apply for loop as follows which will read one column apply the filter and then store the values and then moves to the next column.
X = reshape(T_hor,[],28); % forming 4096x28 matrix
for i = 1:28;
Xnew = X(:,i) - mean(X(:,i)); % filter for DC offset
It just reads the last column (28th) and stops. Is something wrong with my code? Can someone help me to fix this. Thanks in advance.
thanks in advance

Risposta accettata

Greig il 17 Feb 2015
Xnew is not indexed. You should have Xnew(:, i).
You could do this without the loop. One such way would be...
Xnew = X - repmat(mean(X), 4096, 1);
Another is....
Xnew = detrend(X,0);
I would go with the second (less typing), but either will save you some time in a loop.
  7 Commenti
Bharath il 19 Feb 2015
Modificato: Bharath il 19 Feb 2015
Thanks a ton. It was very informative and it works perfectly..! :) So is it always good to preallocate before start of a loop? In my previous case I just defined as
ii= 1:28
It just read only the last column but now it seems working perfectly good with the preallocation.
Greig il 19 Feb 2015
Your loop read through all of the columns, but since Xnew was overwritten each time, it only remembered the last loop.

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