How can I extract coordinates (x,y,z) from a matrix that match coordinates in another matrix

Hi

I have a matrix (A) containing columns for coordinates (x,y,z) and a columns with simulated values (v) for each point. I also have a matrix (B) containing coordinates (x,y,z)for a reference data set which is much smaller.

I would like to remove all rows (points) in matrix A which don't have the same coordinates as in matrix B so that i have a matrix containing x,y,z,v for each point that is included in matrix B.

I also like to state that i have tried to use ismember and intersect for this but it does not give me the same amount of points that is given in matrix B.

Any easy way to solve this?

[madhan ravi]

example?

Answer 1

[Nicola Bombace]

I think that the problem might be that your number are doubles. I suggest an approach based on distance.

You could first use the function pdist2(A,B) which will compute the distance between every point of A and B in a matrix. Then filter the results.

A = [1, 1 , 1; 
     2, 2 , 2; 
     3, 3 , 3; 
     4, 4,  4;
     5,  5,  5];

B = [3 , 3, 3;
     5,  5, 5];

tol = eps;
dist = pdist2(A,B);
samePoints = dist < eps;
rowIndexSamePoint = find(logical(sum(samePoints,2)) > 0);
AFilt = A(rowIndexSamePoint,:);  % A and B are the same matrix

[merialu]

Hi, Thank you for a quick answer.

Although my problem still remains. My matrix A look like your exempel but also have a fourth column with the values that i want to extract. So it looks somehting like this:

A = [1,1,1,7;2,2,2,4;3,3,3,9;4,4,4,2;5,5,5,6]

and B = [3,3,3;5,5,5]

What i want is to extract value 9 and 6 from the fourth column in A.

Any idea?

Thanks

[Nicola Bombace]

With the matrices in your case:

tol = eps;
dist = pdist2(A(:,1:3),B);
samePoints = dist < eps;
rowIndexSamePoint = find(logical(sum(samePoints,2)) > 0);
AVals = A(rowIndexSamePoint,4);

[merialu]

Yes, It works well!

Thank you for all your help, really appreciate it.

[Nicola Bombace]

I am glad to hear that. Happy coding!