Calculate distance between vectors and generate a distance matrix

Hello,

My problem is that I have a file with a collection of features vectors extracted from images and I need to calculate the distances between all the vectors, pair by pair, generating a distance matrix. So, if I have have 100 elements, I need to obtain a 100x100 matrix. Anybody can help me?

Thanks.

Answer 1

[Azzi Abdelmalek]

%Example

v1=randi(10,100,1);
v2=randi(10,100,1);
%--------------------------------
[ii,jj]=ndgrid(v1,v2);
out=reshape(jj(:)-ii(:),100,100);

Answer 2

[Matt J]

The advantage of the following is that it uses BSXFUN, avoiding the creation of intermediate matrices. There are also fancier versions on the FEX, e.g.,

http://www.mathworks.com/matlabcentral/fileexchange/18937-ipdm-inter-point-distance-matrix

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,M]=size(A);
B=reshape(B,N,1,[]);

Graph=l2norm(bsxfun(@minus, A, B),1);

Graph=reshape(Graph,M,[]);

if noself
    n=length(Graph);
   Graph(linspace(1,n^2,n))=nan; 
end

function out=l2norm(X,varargin)
%out=l2norm(X,varargin)
%
%Takes the L2 norm along desired dimensions of the array X.
%
%VARARGIN can be any of the additional arguments of the sum.m function
%and follows the same conventions as this and similar functions. That is, 
%if VARARGIN={}, the function operates along the first non-singleton 
%dimension, etc...
%
%SEE ALSO sumsq

X=X.^2;

out=sum(X,varargin{:});

out=sqrt(out);