Finding nearest values in two matrices

Hi all,

I have two matrices of diffent size, e.g. A= n x 3 and B = m x 3. The first column for both of them represents the depth taken by downhole survey.

If I show you soe part from two matrices, it can be something like:

A:                             B: 
100    0    0               100    0        0
125    1    1               149    1.9    1.9 
150    2    2               181    3.2    3.2        
175    3    3               200    4.4    4.4        
200    4    4             ...
...

It is, the records are taken at slightly different depths and might less/more frequent.

I would like to work based on the depth of the shortest matrix (let's say it's B). I need to create a loop perhaps, so it reads every depth input in the matrix and finds the closest value in the longest matrix. For example, for i =1, corresponding value of 100 (B) would be also 100 (A). For i = 2, corresponding to 149 (B) would be 150 (A), and so on until it ends, saving the corresponding values in columns 2 & 3.

In the end it would generate me a shorter version of matrix A, for every index matching the value in B, such that:

A:                             B: 
100    0    0                100    0        0
150    2    2                149    1.9    1.9 
175    3    3                181    3.2    3.2        
200    4    4                200    4.4    4.4        
 ...

Can be two separate matrices as above or combine into one C = m x 6.

I would appreciate some help. Thanks!

Answer 1

[Adriano Filippo Inno]

Hi John, the following do what you asked using min:

 a = A(:,1);
 b = B(:,1);
 
 Nb = length(b);
 A_new = zeros(Nb,3);
 for i = 1:Nb
     [~,index] = min(abs(a - b(i)));
     A_new(i,:) = A(index,:);
 end