Find whether a vector occurs exactly in another vector

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Hi,
I try to compare two vectors (waveforms from wav files). One is the original sound file and the other is a manipulated sound file. I try to find the indices in the original sound file that match with the manipulated sound file. In the end, I would like to plot the original sound file and highlight the parts that were manipulated.
Loading the files into Matlab is no problem, but finding a way to compare/match the files is difficult. I tried the "ismember" function, but I think this function will try to find a match for each datapoint whereas I need something that matches a complete vector with original sound files.
Any suggestion on how to find whether a small vector occurs exactly in another longer vector?
Best, Mark

Accepted Answer

Guillaume
Guillaume on 29 Jan 2015
Surprisingly enough, strfind works on numerical arrays as well and does exactly what you need:
x = [4 3 1 7 36 4 2 3 1 2 58 8 4 6 99 4 3 2 1 5 7 6 4 1 8 4 6 99 4 3 2 1 3 9 7 7 4 3 5];
y = [8 4 6 99 4 3 2 1]; %occurs at position 12 and 25 in x
pos = strfind(x, y)
  2 Comments
Guillaume
Guillaume on 29 Jan 2015
I think that's indeed on Loren's blog that I first came across it.

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More Answers (2)

Eric G.
Eric G. on 29 Jan 2015
This may be a brute force way but MATLAB should be able to handle it with no problem.
Just scan the shorter vector across the longer one and compare for equality.
x= [4 3 1 7 36 4 2 3 1 2 58 8 4 6 99 4 3 2 1 5 7 6 4 1 3 9 7 7 4 3 5];
y = [8 4 6 99 4 3 2 1];
ny = length(y);
for k = 1:(length(x)-ny+1)
check = x(k:k+ny-1)== y;
if sum(check) == ny
fprintf('Found a match at k = %2.0i \n',k)
end
end

Andrei Bobrov
Andrei Bobrov on 29 Jan 2015
Edited: Andrei Bobrov on 29 Jan 2015
other variant
n = numel(y);
pos = find(all(bsxfun(@eq,y(:),hankel(x(1:n),x(n:end)))));

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