Get certain matrix entries to a new matrix

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.

[tareq ALTALMAS]

can you please explain more

for example 2nd line how it became 2005 2005 and the last 2 lines also

[Rene]

There was one mistake in the second matrix (as you saw with the 2005 2005).

The numbers are measurement points on a model. The first table/matrix gives the information which point connects to others.

Later all of the points will get x,y and z values to then plot a vector from point to point to get a 3d line model.

Therefore I need to extract the connections.

2003 connects to 2004 and no other

3001 connects to 3002, 5002 and 6002.

Is it any clearer now?

Answer 1

[dpb]

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
>> 

[Rene]

Thank you very much. This pretty much worked out.

The only little problem is, that in my full matrix are some points that are a "dead end". So they have no connection at all. They stil appear in the new matrix with a zero.

[dpb]

You mean there's one or more nodes with a zero in column 2? If that's so, just remove them first...

A(A(:,2)==0)=[];

before the previous code.

Or after gets to same end but first is more efficient in reducing the size quicker.

[dpb]

Or, save only those w/ a node connection first...

A=A(A(:,2)~=0);