Finding small vector in big vector

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Lennart
Lennart 2015-10-20
编辑： Bruno Luong 2024-5-12
Hey everybody,
I am desperately looking for a function that can find a small vector inside a big vector. Ismember and interesect just wouldn't do it right :(
Let's say I have the two vectors x = [ 7 6 9 7 4 3 7 9 0 7 4 3 2 6 7 0 7 5 ]; y = [ 4 3 2 6 ]
As a result I would like to have ans = [ 11 12 13 14 ]
so only the coordinates of where the values are in the correct sequence. Is there anything that can do that?
Thanks in advance!

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采纳的回答

Image Analyst
Image Analyst 2015-10-20
Try this:
x = [ 7 6 9 7 4 3 7 9 0 7 4 3 2 6 7 0 7 5 ];
y = [ 4 3 2 6 ];
% As a result I would like to have ans = [ 11 12 13 14 ]
out = strfind(x, y) + [0:length(y)-1]
  2 个评论
Lennart
Lennart 2015-10-21
编辑：Image Analyst 2015-10-21
Wohoo awesome. Thank you guys so much! That just works perfectly. Actually the strfind itself is just what I need, but the idea of "+[0 : length(y)-1] " is quite needed as well.
Image Analyst
Image Analyst 2015-10-21
You're welcome. strfind(x, y) finds only 11 - the start of the sequence - while adding that other vector gives you [11,12,13,14] which is what you said you wanted.

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更多回答（2 个）

James Tursa
James Tursa 2015-10-20
编辑：James Tursa 2015-10-20
I am not on a machine with MATLAB at the moment to test this, but maybe try the strfind(x,y) function to see if it works with doubles (even though the doc doesn't indicate that it does).
  3 个评论
显示 1更早的评论
Bruno Luong
Bruno Luong 2022-9-12
编辑：Bruno Luong 2024-5-12
Ran in:
@Alexander Paul "The numbers are internally casted to char."
I don't think so, if it was, the result of the two last commands would be indentiical
d = double('a')+0.1;
a = 'a';
strfind(d,a)
ans = []
strfind(char(d),char(a))
ans = 1
Alexander
Alexander 2022-9-12
You are right. I checked it only with uint8.

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Matlab Pro
Matlab Pro 2024-5-12
Hi
A small improvement where the sub-vector is found more than once...
x = x(:)'; % Make sure data is a Row vector
ix = strfind(x, y);
if length(ix)>1 % Fix cases where y is found more than once
idx = [1:length(y)] + ix(1)-1; % Indexes of 1st occurance
else
idx = strfind(x, y) + [0:length(y)-1];
end

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