List of Node pairs

How can I get a matrix of node pairs from a graph? That is, if there are 4 nodes 1,2,3,4, then the node pair matrix would be :

1 2

1 3

1 4

2 1

2 3

2 4

3 2 etc.

I could do this using 2 for loops, but is there any quick way of doing it?

[Akira Agata]

Questions for clarification:

• You want to obtain node pair matrix from graph object ?
• If the graph has an edge from node m to node n, you need both (n, m) and (n, m) in your matrix?

[Hari]

Sorry if the question was confusing. I need to get the list of node pairs but it need not be from the graph object. Knowing the number of nodes in the graph would be sufficient I guess. If there are 4 nodes in the graph then the output should be:

1 2

1 3

1 4

2 1

2 3

2 4

3 1

3 2

3 4

etc..

The edges in the graph is not important here.

Answer 1

[Akira Agata]

Another possible solution:

numNode = 4;
[r,c] = find(~eye(numNode));
v = [c,r];

>> v

v =

1 2

1 3

1 4

2 1

2 3

2 4

3 1

3 2

3 4

4 1

4 2

4 3

Answer 2

[Simon Chan]

Basically you just want to create the matrix, right?

u=1:4;
u_entend = repelem(u,1,length(u)-1);
w = repmat(u',1,length(u));
v = reshape(tril(w,-1) + triu(w,1),1,[]);
v = v(v~=0);
node_pair = [u_entend;v]'

Result:

node_pair =

     1     2
     1     3
     1     4
     2     1
     2     3
     2     4
     3     1
     3     2
     3     4
     4     1
     4     2
     4     3

Answer 3

[Walter Roberson]

u=1:4;
[s,t] = ndgrid(u);
v = [s(:),t(:)];
mask = v(:,1) ~= v(:,2);
v = v(mask,:);

v

v = 12×2

2 1 3 1 4 1 1 2 3 2 4 2 1 3 2 3 4 3 1 4