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POHow to resample with interp1 in Matlab when input vectors are of different length
 

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  1. POHow to resample with interp1 in Matlab when input vectors are of different length
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    <p>I have two variables in a .mat file here: <a href="https://www.yousendit.com/download/UW13UGhVQXA4NVVQWWNUQw" rel="nofollow">https://www.yousendit.com/download/UW13UGhVQXA4NVVQWWNUQw</a></p> <p>testz is a vector of cumulative distance (in meters, monotonically and regularly increasing)</p> <p>testSDT is a vector of integrated (cumulative) sound wave travel time (in milliseconds) generated using the distance vector and a vector of velocities (there is an intermediate step of creating interval travel times)</p> <p>Since velocity is a continuously variable function the resulting interval travelt times and also the integrated travel times are non integers and variable in magnitude</p> <p>What I want is to resample the distance vector at regular time intervals (e.g. 1 ms, 2 ms, ..., n ms)</p> <p>What makes it difficult is that the maximum travel time, 994.6659, is less than the number of samples in the 2 vectors, therefore it is not straightforward to use interp1. i.e.:</p> <p>X=testSDT -> 1680 samples</p> <p>Y=testz -> 1680 samples</p> <p>XI=[1:1:994] -> 994 samples</p> <p>This is the code I've come up with. It is a working code and it is not too bad I think.</p> <pre><code>%% Initial chores M=fix(max(testSDT)); L=(1:1:M); %% Create indices % this loops finds the samples in the integrated travel time vector % that are closest to integer milliseconds and their sample number for i=1:M [cl(i) ind(i)] = min(abs(testSDT-L(i))); nearest(i) = testSDT(ind(i)); end %% Remove duplicates % this is necessary to remove duplicates in the index vector (happens in this test). % For example: 2.5 ms would be the closest to both 2 ms and 2 ms [clsst,ia,ic] = unique(nearest); idx=(ind(ia)); %% Interpolation % this uses the index vectors to resample the depth vectors at % integer times newz=interp1(clsst,testz(idx),[1:1:length(idx)],'cubic')'; </code></pre> <p>As far as I can see there is one issue with this code: I rely on the vector idx as my XI for interpolation. Vector idx is 1 sample shorter than vector ind (one duplicate was removed).</p> <p>Therefore my new times will stop one millisecond short. This is a very small issue, and duplicate are unlikely but I am wondering if anybody can think of a workaround, or of a different way to approach the problem altogether.</p> <p>Thank you</p>
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