Apply a filter to a dataset of ecg signals

I have a dataset of 48 ECG signals (attached here as a zip file, but I use it unzipped), placed in a directory. I have use a for-cicle to load all the signal in the workspace, but now I am a bit confunsed.

I want to apply to the signals a Band-Pass Butterworth filter, so I use butter to design the filter and filtfilt to apply it. But I have a problem with size in "y(i)". This is the error I get:

"Unable to perform assignment because the indices on the left side are not compatible

with the size of the right side."

this is my code:

Fs = 360; % sample frequency of signals [Hz]

files = dir(fullfile("dataset/","*.mat"));
for i = 1:numel(files)
    data(i) = load(files(i).name); % load signals
    [b,a] = butter(3,[1 30]/(Fs/2),"bandpass"); % bandpass butterworth filter of third order with 1-30 Hz 
    y(i) = filtfilt(b,a,data(i).val); % apply the filter to all signals 
end

Answer 1

[Karim]

Hello, the problem is that you didn't initalize the variable "y". Hence you are trying to fit an array of 1x3600 into a single position (i.e. y(i) ).

See below for a quick fix:

files = dir(fullfile("dataset/","*.mat"));

Fs = 360; % sample frequency of signals [Hz]
[b,a] = butter(3,[1 30]/(Fs/2),"bandpass"); % bandpass butterworth filter of third order with 1-30 Hz 

y = zeros(numel(files), 3600);
for i = 1:numel(files)
    data(i) = load(fullfile("dataset/",files(i).name)); % load signals
    y(i,:) = filtfilt(b,a,data(i).val); % apply the filter to all signals 
end

[Sabaudian]

thank you