I have 2 matrices, containing x,y data, how do i find the closest point and extract data about that point?

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Richard Sims
Richard Sims 2013-1-29
评论： sensation 2017-2-7
Hey matlabians!
A is a matrix with two columns, A= [X,Y], that give the position x and y.
B is a matrix with 3 columns,B=[X,Y,P], the position x and y, and P is simply a value assigned to that position in space.
I could use a nearest neighbour search to find the value of B closest to A, what i actually want is for every point A find the closest B and give A the value of P.
I have seen nearest neighbor analysis attempted elsewhere but that has always been for one dataset, is there a command for this? does anyone have any help, it would help me out no end. Many thanks Rich
  2 个评论
Image Analyst
Image Analyst 2013-1-29
Is B a 3D matrix, or an N rows by 3 column matrix? What does P represent? A Z value? If the Pythagorean theorem of any use to you?
Richard Sims
Richard Sims 2013-1-29
编辑：Richard Sims 2013-1-29
A is a matrix with two columns, that give the position x and y.
B is a matrix with 3 columns, the position x and y, and P is simply a value assigned to that position in space.
I could use a nearest neighbour search to find the value of B closest to A, what i actually want is for every point A find the closest B and give A the value of P.
I apologize if my question wasn't clear before

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采纳的回答

Shashank Prasanna
Shashank Prasanna 2013-1-29
Why don't you use knnsearch in MATLAB and the indices of the point that is closest in B that in A, and use the index to extract the P value.
IDX = knnsearch(B(:,1:2),A)
B(:,IDX)
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Richard Sims
Richard Sims 2013-2-2
编辑：Richard Sims 2013-2-2
do you perhaps know anyway of altering this code to find the nearest neighbor if A and B were latitude and longitudes?
The stdist command works using latitude and longitude distances but then i wouldn't be able to index the data any longer like in your example above. The knnsearch help box says it accepts custom distance functions but i don't seem to be able to find one. Sorry to keep bothering you!
sensation
sensation 2017-2-7
Hi, what about finding the neareast number and its id betweeen two different size arrays?
for instance, I have an array: A: 540x1 values; and another array B, 540 X 4860 consisted of 540 blocks (each one represented by 3x3 matrix-so 9X540=4860).
What I want to do is to search through each of these 9 area block numbers, compare it with single number from B and retrieve that area.
A: 45 etc X 540
B: 5 6 9
4 15 16
21 55 2
etc X 540 blocks like this;
result: would be 55 and id=8 since the counting in my code goes like:
234
516
789 Thanks a lot for any tip!

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更多回答（3 个）

Sean de Wolski
Sean de Wolski 2013-1-29
How about using dsearchn() to find the nearest neighbors?
doc dsearchn
Matt J
Matt J 2013-1-29
  2 个评论
Richard Sims
Richard Sims 2013-1-29
If the two matrices were A= [X,Y], B=[X,Y] then i think this solution would be perfect for determining the distances.
However i want to find the value P from matrix B and assign it to A and i don't believe this works for such a problem A= [X,Y], B=[X,Y,P]
Matt J
Matt J 2013-1-29
编辑：Matt J 2013-1-29
You can also use the tool to obtain the indices i, of the distance minimizing B(i). Just get the associated P(i) from that. Here's a way you can do it using my more crude distance matrix tool below
D=interdists([Ax(:),Ay(:)].', [Bx(:), By(:)].');
[~,imin]=min(D,[],2);
P_of_A=P(imin);
function Graph=interdists(A,B)
%Finds the graph of distances between point coordinates
%
% (1) Graph=interdists(A,B)
%
% in:
%
% A: matrix whose columns are coordinates of points, for example
% [[x1;y1;z1], [x2;y2;z2] ,..., [xM;yM;zM]]
% but the columns may be points in a space of any dimension, not just 3D.
%
% B: A second matrix whose columns are coordinates of points in the same
% Euclidean space. Default B=A.
%
%
% out:
%
% Graph: The MxN matrix of separation distances in l2 norm between the coordinates.
% Namely, Graph(i,j) will be the distance between A(:,i) and B(:,j).
%
%
% (2) interdists(A,'noself') is the same as interdists(A), except the output
% diagonals will be NaN instead of zero. Hence, for example, operations
% like min(interdists(A,'noself')) will ignore self-distances.
%
% See also getgraph
noself=false;
if nargin<2
B=A;
elseif ischar(B)&&strcmpi(B,'noself')
noself=true;
B=A;
end
N=size(A,1);
B=reshape(B,N,1,[]);
Graph=l2norm(bsxfun(@minus, A, B),1);
Graph=squeeze(Graph);
if noself
n=length(Graph);
Graph(linspace(1,n^2,n))=nan;
end

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sensation
sensation 2017-2-7
Hi, what about finding the neareast number and its id betweeen two different size arrays?
for instance, I have an array: A: 540x1 values; and another array B, 540 X 4860 consisted of 540 blocks (each one represented by 3x3 matrix-so 9X540=4860).
What I want to do is to search through each of these 9 area block numbers, compare it with single number from B and retrieve that area.
A: 45 etc X 540
B: 5 6 9
4 15 16
21 55 2
etc X 540 blocks like this;
result: would be 55 and id=8 since the counting in my code goes like:
234
516
789

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