Nearest Neighbor Matching without Replacement

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Al
Al 2016-12-7
回答： Bruno Luong 2022-2-25
Hello there,
I am looking to match data in two vectors, x and y, based on shortest Euclidean distance. Each match should be unique; that is, numbers in vectors x and y cannot be matched twice. I have looked into knnsearch, but have not found anything that suggests the function works without replacement. Thank you!
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Phillip
Phillip 2018-3-30
It does not violate the shortest distance if it is removed from the set once matched (what Al is referring too when he says " without Replacement").
Peng Li
Peng Li 2020-3-31
any update here? also was wondering if there is a way to do knn search without replacement.

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回答（2 个）

neuroDuck
neuroDuck 2022-2-25
A late response, but for anyone that might come across this in future, I think a brute force approach should work, with the following code, assuming you don't have too many comparisons to go through:
[cIdx] = unique(knnsearch(x,y));
% brute force knnsearch to do without replacements
startingK = 2;
while length(cIdx)<length(y)
[cIdx] = unique(knnsearch(x,y,'k',startingK));
startingK = startingK + 1;
end
Bruno Luong
Bruno Luong 2022-2-25
Ran in:
If you have R2019a release
x=rand(1,10)
x = 1×10
0.7999 0.9374 0.3693 0.3038 0.4504 0.9999 0.9559 0.9041 0.6531 0.1136
y=rand(1,10)
y = 1×10
0.2727 0.5885 0.7090 0.6540 0.6661 0.3712 0.2943 0.0732 0.8695 0.5349
C=abs(x(:)-y(:).');
M = matchpairs(C,max(C(:)));
px = M(:,1);
xm = x(px)
xm = 1×10
0.3693 0.6531 0.9999 0.7999 0.9559 0.4504 0.3038 0.1136 0.9374 0.9041
d = abs(xm-y)
d = 1×10
0.0966 0.0646 0.2910 0.1459 0.2898 0.0792 0.0094 0.0404 0.0679 0.3692

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