Find whether a vector occurs exactly in another vector

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

Answer 1

[Guillaume]

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)

[Cedric]

+1 This has been discussed a few times by Loren, for example here.

[Guillaume]

I think that's indeed on Loren's blog that I first came across it.

Answer 2

[Eric G.]

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

Answer 3

[Andrei Bobrov]

other variant

n = numel(y);
pos = find(all(bsxfun(@eq,y(:),hankel(x(1:n),x(n:end)))));