MATLAB: Get certain matrix entries to a new matrix

Question

Hello

I need to create a loop that reads certain data from a matrix and put it into a new matrix.

The matrix is for example:

2003    2004    0          0          0
2004    2005    0          0          0
2005    4005    0          0          0
3001    3002    5002    6002          0

Now I want to automatically create a new matrix that gives me all the "connections" like so:

2003    2004
2004    2005
2005    4005
3001    3002
3001    5002
3001    6002

Zeros should be ignored in the new matrix. The first column is always filled with a number.

Any idea how to do this? I'm thinking of a while loop but I can't figure out how.

Answer 1

Sometimes, just "dead ahead" is as good as any...

nAdd=sum(A~=0,2)-2;                 % number of connections beyond the one for each first node
V=zeros(size(A,1)+sum(nAdd),2);     % preallocate for final array
% the engine...
j=0;
for i=1:size(A,1)
  j=j+1;
  V(j,:)=A(i,1:2);
  for k=1:nAdd(i)
    j=j+1;
    V(j,:)=[A(i,1),A(i,2+k)];
  end
end

above results in

>> V
V =
        2003        2004
        2004        2005
        2005        4005
        3001        3002
        3001        5002
        3001        6002
>>