Remove node and reconnect edges in graph

I have a node in a graph that acts as a sort of 'temporary connector' node. I'd like to remove that node and update the edges in the graph so that all of its immediate predecessors point to its immediate successors.

Example: I have a graph 1 > 2 > 3. I'd like to remove node 2 and end up with the graph 1 > 3.

I read several posts on removing nodes, but couldn't find a way to do what I want.

Answer 1

[Chunru]

s = [1 1 1 1 2 2 3 3 3 5 5];
t = [2 3 4 6 1 5 4 5 6 4 6];
names = string(1:6);
G = digraph(s, t, [], names);

h1 = plot(G);

% Remove node and add the eages
% node 1
G1 = G;
pre = predecessors(G1, 1);
suc = successors(G1, 1);
for i=1:length(pre)
    for j=1:length(suc)
        G1=addedge(G1, pre(i), suc(j));
    end
end
G1 = rmnode(G1, 1);   % remove the node 1 also remover the edges to 1
%G.Edges, G1.Edges
figure 
h2 = plot(G1);
h2.XData = h1.XData(2:end);
h2.YData = h1.YData(2:end);

[IrisL]

Thanks for your answer. That helps a lot. I am wondering if this can also be done for nondirect graph. Removing node and reconnecting edges for graph without direction.

[Chunru]

Yes. It can be definetely done with the same idea. Instead of finding the predecessors and successors, you need to find the neighbours. Then you need to add edges to each pairs of neighbours of the node to be removed (you may need to check if the edge to be added is already in the original graph).

[IrisL]

So I guess I can use one for loop instead of two for loop to do this.

[Chunru]

You may still need two for loops:

for i=1:length(nb)  % nb: neighbors
    for j=i+1:length(nb)
        ....
    end
end

[IrisL]

Thanks. You mentioned checking if the edge to be added is alrready in the original graph. Do you have any suggestion on doing so (and potentially removing those duplicated edges)? I saw people using 'unique(sort(EdgeList,2),'rows')'. But I have the edges as a table instead of list.

[Chunru]

unique(G.Edges) should work for an Edge Table G.Edges

[IrisL]

I used unique(G.Edges.EndNodes) which returns a seperate cell with unique edges. However, this code does not remove duplicate edges from the graph. The number of the edges will not change and G.Edges remains the same.