MATLAB: For many vectors of data of different length, how to interpolate to set them all to have the same length

datainterpolationMATLAB

I'm analyzing a series of data vectors, each of which has a different number of points, but the x-coordinate of the data spans 1 to ~2800. My simulations have 1400 points, so I need to interpolate the data vectors to properly sample the y-coordinate of the data while ending up with all interpolated data vectors at a length of 1400. Are there any helpful tricks? I know "resample()" would do the trick, but I'm not able to purchase the signal processing toolbox, so that's not an option.

Best Answer

Use interp1()

Demo:

xdata = 1:280; 
ydata = 10:150; 
xdataResamp = linspace(xdata(1),xdata(end),numel(ydata)); 
ydataInterp = interp1(xdataResamp,ydata,xdata); 
% Visually inspect results
figure()
plot(xdataResamp,ydata, 'b-o')
hold on
plot(xdata, ydataInterp, 'r-s')

Related Solutions

MATLAB: How to find the peaks of a cfit object

test.coefs is giving you the coefficients of the cubic splines that make up the fit. If I interpret your intention correctly, you're wanting the actual fitted curve. To do that, use feval:

yFitted = feval(fit,xData);

Now you can use findpeaks on yFitted (assuming that yData was a vector originally, so this is a 1-D fit).

xData = sort(rand(295,1));
yData = sin(6*pi*xData) + 0.1*randn(295,1);
ft = fittype( 'smoothingspline' );
opts = fitoptions( 'Method', 'SmoothingSpline' );
opts.SmoothingParam = 0.9999;
[fitresult, gof] = fit( xData, yData, ft, opts );
yfitted = feval(fitresult,xData);
plot(xData,yData,xData,yfitted)
[ypk,idx] = findpeaks(yfitted);
xpk = xData(idx);
hold on
plot(xpk,ypk,'o')

MATLAB: Interpolating Data from Vectors of Different Length

This is a job for the interp1 function:

% Make original data
oldPcntVals = [0 .1 .3 .7 .9 1];
oldYvals = [10 12 15 13 12 11]
% Set a new spacing from 0 to 1 and interpolate
newPcntVals = 0:0.02:1;
newYvals = interp1(oldPcntVals, oldYvals, newPcntVals);
% Compare the original values to these interpolated values
figure
plot(oldPcntVals, oldYvals, 'b.', newPcntVals,newYvals, 'g')

Keep in mind that the default interpolation method for interp1 is "linear". You could also set "cubic" or "spline" if you wanted to have your final output smoothly interpolate between your original data.

Best Answer

Related Solutions

MATLAB: How to find the peaks of a cfit object

MATLAB: Interpolating Data from Vectors of Different Length

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