# Finding the index of elements of a vector in a mesh quite fast

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Mohammad Shojaei Arani on 7 Jun 2022
Hello friends,
I would like to find the index of vector of numbers A being closest in a mesh. I know how to do this but I hope you have a better idea to speed up the calculations.
An example: Consider a mesh of 10^6 regularly spaced numbers in the interval [0 10] and 10^4 random points A in this interval and we wish to find their corresponding index in our mesh (in the sense of being closest).
mesh=linspace(0,10,10^6);
A=0+(10-0).*rand(1,10000);
N=1000;
tic;
for n=1:N
ind=interp1(A,1:length(A),mesh,'nearest');
end
t=toc;
t/N
ans =
0.016923
So, on average it takes around 0.016923 seconds. I think that there should be a very smart way to do the same task with a much reduced computational time.
Any idea is greatly appreciated!
Babak
##### 2 CommentsShowHide 1 older comment
Mohammad Shojaei Arani on 7 Jun 2022
Yes, of course. I was not carefull

Torsten on 7 Jun 2022
Edited: Torsten on 7 Jun 2022
mesh=linspace(0,10,10^6);
A=0+(10-0).*rand(1,10000);
N=1000;
tic;
for n=1:N
y = discretize(A,mesh);
idx = A-mesh(y) >= mesh(y+1)-A;
y(idx) = y(idx) + 1;
end
t=toc;
t/N
ans = 0.0024
Mohammad Shojaei Arani on 7 Jun 2022
Great man!
I am happy with this!

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