# List of Node pairs

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Hari on 15 Jul 2021
Answered: Akira Agata on 16 Jul 2021
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?
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Hari on 16 Jul 2021
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.

Akira Agata on 16 Jul 2021
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

Simon Chan on 16 Jul 2021
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

Walter Roberson on 16 Jul 2021
u=1:4;
[s,t] = ndgrid(u);
v = [s(:),t(:)];
v
v = 12×2
2 1 3 1 4 1 1 2 3 2 4 2 1 3 2 3 4 3 1 4