I have a rather large matrix. The data was sampled at 100 Hz. I want to the data to look like it was sampled at 5 Hz

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Todd
Todd on 17 Aug 2012
Right now the left column is time and it counts .01, .02, .03 etc.
I want to pull out all of the data at 5 hz intervals such as 0, .2, .4 and delete the rest of the rows.
I will answer any question for clarification too
  4 Comments
Jürgen
Jürgen on 18 Aug 2012
yeah all right all depends on what you are measuring and the first thing to do is to analyse your data in a smart way of course, but let us say that you are doing e.g. loadcell measurements over time to see how a the force changes, you will have noise on the measurement and the average will gie you an idea how the signal moves in time , that is what I meant

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Answers (4)

Jürgen
Jürgen on 17 Aug 2012
well If I understand it well you have a vector Sample100 with 100 Hz Samples and you want only the sample @ 5 hz Sample5=Sample100(1:20:end) should do the trick then hope this helps regards,J

Azzi Abdelmalek
Azzi Abdelmalek on 17 Aug 2012
Edited: Azzi Abdelmalek on 17 Aug 2012
fe=100 %sample frequency
te=1/fe %sample time
t=0:te:1;y=rand(length(t),1)%
fd=5 %desired frequency
td=1/fd %desired sample time
nt=floor(td/te)
ind=1:nt:length(t);
new_t=t(ind);
new_y=y(ind);
plot(t,y);hold on;plot(new_t,new_y,'xr','linewidth',14);

Matt Fig
Matt Fig on 17 Aug 2012
Here is another example. You say the first column is time, so it is here.
% Original data with columns: [time,signal]
S = [(0:.01:2*pi).' sin(0:.01:2*pi).'];
Sd = S(1:20:end,:); % Downsampled signal.
plot(S(:,1),S(:,2),'b.',Sd(:,1),Sd(:,2),'sr')
legend('Original','Downsampled')

Dr. Seis
Dr. Seis on 17 Aug 2012
Edited: Dr. Seis on 17 Aug 2012
Use resample - This is an example of why you may not want to take every Nth amplitude:
Example where a is your input dataset and b is your output dataset:
Fs_in = 100; % samples per second
Fs_out = 5; % samples per second
b = resample(a,Fs_out,Fs_in);

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