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
end;
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
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Greig
2015-2-17
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 个评论
Bharath
2015-2-18
Ilham Hardy
2015-2-18
The answer is on the error message, you want to put data into second column of X, hence X(:,2) , which does not exist since the size of X is 4096x1 (array, not matrix/table).
Bharath
2015-2-18
Greig
2015-2-19
If you really insist on using a loop try this....
X=rand(4096, 28); % My test data
Xnew = NaN(size(X)); % Preallocate for speed
for ii=1:size(X, 2)
Xnew(:,ii) = X(:,ii) - mean(X(:,ii));
end
[It is recommended not to use "i" or "j" as an indices given that they are sqrt(-1).]
Then compare with these...
Xnew2 = X - repmat(mean(X), size(X, 1), 1);
Xnew3 = detrend(X,0);
Of course if you want to apply more complicated filters than mean subtraction, the loop version may be the better option.
Greig
2015-2-19
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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