# Compare two vectors for similarity

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Souparno Bandyopadhyay il 9 Dic 2012
Commentato: maxanto il 2 Feb 2022
How to compare two vectors quickly. Right now I print out each in a loop and examine them by eye, is there a way i can find if two are almost similar.
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Souparno Bandyopadhyay il 9 Dic 2012
I am comparing A to B and then A to C, I need a single number that will allow me to quickly judge A resembles B or C.
maxanto il 2 Feb 2022
isequal(a, b)
Returns true if each element of vector a is equal to each element of vector b. If some element of a are different from b returns false.

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### Risposta accettata

Matt Fig il 9 Dic 2012
What is the criteria for 'almost similar' in your application? 90% same exact values? 90% of the values in one vector within 95% of some other value in the other vector? Do the values have to be in the same positions? Do the vectors have to be the same length? Perhaps a few short examples would help...
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Jan il 9 Dic 2012
@Souparno: Accepting an answer means that the problem is solved. Is this true here?
Souparno Bandyopadhyay il 10 Dic 2012
yes, S = sum(A-B), is what I was looking for.

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### Più risposte (1)

Greg Heath il 10 Dic 2012
S = sum(A-B) is NOT a useful function for quantifying similarity because positive and negative terms will cancel.
The most common are
mae(A-B) % mean(abs(A-B))
sae(A-B) % sum(abs(A-B))
norm(A-B,1) % sum(abs(A-B))
norm(A-B,inf) % max(abs(A-B))
mse(A-B) % mean((A-B).^2)
sse(A-B) % sum((A-B).^2)
norm(A-B) % sqrt(sse(A-B))
Hope this helps.
Thank you for formally accepting my answer
Greg
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