MATLAB Answers

choose data points that nears each other and store in different matrix

1 view (last 30 days)
Laura
Laura on 17 Jul 2013
I have a matrix A that has dimension n x 2.
A(:,1) is x-values and A(:,2) is y values.
Choose the the pairs that is near each others within certain distance and store in matrix B that has x value in column 1 and y value in column 2.
Example
A= [1 1 ; 2 2 ; 5 5 ; so on]
let say if the distance we want to set is 2
then dist =sqrt((2-1)^2 +(2-1)^2) = sqrt(2) which is less than 2. So first and second pair are close.
store it in B
B= [1 1 ; 2 2; so on ]
Nothe this is example for 3 pairs and I have n- pair.
Please help me with a loop to do n-pair
Thank you

Accepted Answer

Matt Kindig
Matt Kindig on 17 Jul 2013
Edited: Matt Kindig on 17 Jul 2013
One (non-loop) way:
[x1,x2]=meshgrid(A(:,1));
[y1,y2]=meshgrid(A(:,2));
D = sqrt((x1-x2).^2+(y1-y2).^2); %distance matrix
setDistance = 2;
[r,c]=find(D <= setDistance); %find which pairs are below setDistance.
B = [r,c]; %set of pairs
B(r==c,:)= []; %eliminate points paired with itself.
  5 Comments
Matt Kindig
Matt Kindig on 18 Jul 2013
Right, but this means that B doesn't indicate any information as to which points are members of which pairs. As it stands now, your B just contains points which are members of a pair which is within 2 units of another point; however, the pair correspondence is not present.
If this is what you wish to do, you can add this line of code to the end:
B = A(unique(B(:)),:);
to get that result.
However, you lose the pair information. Really it depends on what you intend to do with the points in B once you've found them.

Sign in to comment.

More Answers (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by