How to segment data using overlapping window
35 views (last 30 days)
Show older comments
mahrukh jamil
on 6 Oct 2016
Commented: Alistair Steyn-Ross
on 21 Jun 2023
Hello, I have an ECG data of 20mins length (2x307200). I want to apply a 20 sec window(5120) with an overlap of 64samples. I want 20 sec segments so i can extract features from it. I tried to write a loop for window but it doesn't give me right answer. Can somebody help me.
ECG_data=[time; ECG];
N_max=length(ECG_data);
n_window=5120;
overlap_win=64;
count=1;
for n_start = 1:overlap_win:(N_max-n_window)
New_data(count,:) = ECG_data(n_start_1:(n_start+ n_window));
do something..
mean(count,:)=mean(new_data);
count=count+1;
end
The number of samples in each window is limited to 4720 sample(thats 18 sec) even though i need 20sec(5120). What am I doing wrong here? it something to do with the termination of window?? Also how can i retain the time information after applying window?
0 Comments
Accepted Answer
Guillaume
on 6 Oct 2016
Edited: Guillaume
on 6 Oct 2016
Something that's really not clear is that your ECG_data has two rows, yet within your loop you're using linear indexing, which is not consistent. The end result, when n_start is 1 is that New_data(1, :) is [time(1), ECG(1), time(2), ECG(2), ...].
Assuming you only want the second row (ECG) of ECG_data in new_data, a very simple way to create it in one go, without a loop is with:
Matlab R2016b or later only:
new_data = ECG((0:64:307200)' + (1:5120));
Any version of matlab:
new_data = ECG(bsxfun(@plus, (0:64:307200)', 1:5120));
You can do the same with time if needed
8 Comments
Guillaume
on 11 Oct 2016
Note: I made a mistake in the above, there's a -1 that snuck in a few places. I've corrected that now.
As it is the number of windows is:
no_of_windows = max(1 + floor((size(data, 2) - windowlength) / windowstep), 0);
The numbers of columns to add to make sure the last samples are included is:
col_to_add = mod(windowlength - size(data, 2), windowstep);
More Answers (2)
LauraLee Austin
on 6 Oct 2016
It was not clear to me how/where you wanted the overlap. Below is my quick stab at what I think you might be looking for. It is not efficient.
ECG_data=[time; ECG];
N_max=length(ECG_data);
n_window=5120;
overlap_win=64;
max_count = ceil((length(ECG_data)-n_window)/(n_window-overlap_win))+1;
new_data = zeros(max_count,n_window);
n_start=1;
for count = 1:max_count
n_end = n_start + n_window - 1;
if n_end > N_max
new_data(count,1:N_max-n_start+1) = ECG(n_start:N_max);
else
new_data(count,:) = ECG(n_start:n_end);
end
n_start = n_end-overlap_win;
% do something..
end
ECG_mean=mean(new_data');
0 Comments
Fars Samann
on 26 Jun 2022
Simply use buffer.m and define the length of the window and the overlapped part
with regards
Fars
1 Comment
Alistair Steyn-Ross
on 21 Jun 2023
Great suggestion. The 'buffer' function handles overlap, underlap, and no overlap. It's a compiled function (in Signal Processing toolbox) so should run very fast. The built-in documentation illustrates with an informative example:
x = 1:18; % Example input data to be buffered
y = buffer(x, 8, 4); % Create overlapping buffer matrix
See Also
Categories
Find more on Multirate Signal Processing in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!