## How do I filter my data points without using smoothdata?

### Thomas Nell (view profile)

on 11 Dec 2018
Latest activity Edited by Image Analyst

### Image Analyst (view profile)

on 12 Dec 2018
I have 2 variables, t and y, which are both vectors. What I want to do is smooth the data so that, for example, if t is a 10x1 vector, it becomes a 5x1 vector comprising an average of the data points around it. How do I go about this without using the smoothdata function?
Thank you very much and kind regards,
Tom

Bob Nbob

### Bob Nbob (view profile)

on 11 Dec 2018
I'm sure there's a better way, but you could do this manually using a for loop and interpolation.
t2 = linspace(t(1),t(end),5);
for i = 1:5;
y2(i) = interp1(t,y,t2(i));
end

on 11 Dec 2018
Note: Interpolation without smoothing or lowpass filtering first could result in aliasing.

### Tags

on 11 Dec 2018

What about movmean to smooth the data, then interp1 to pick out the 5 points you want?

Thomas Nell

### Thomas Nell (view profile)

on 12 Dec 2018
Is movmean part of the signal processing toolbox??? I'm not allowed to use any functions from there
Image Analyst

### Image Analyst (view profile)

on 12 Dec 2018
No, it's part of base MATLAB. If you get help on any function, it will tell you what toolbox it's in, if any.

### Image Analyst (view profile)

on 12 Dec 2018
Edited by Image Analyst

### Image Analyst (view profile)

on 12 Dec 2018

You could use conv() to smooth y.
windowWidth = 5;
kernel = ones(1, windowWidth) / windowWidth;
smoothedY = conv(y, kernel, 'valid'); % conv() is in base MATLAB.
Do NOT smooth t, for obvious reasons.