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Computer Science Mathematics Mathematica Graphs and Networks Wolfram Language

Get the End Points of an Edge

Posted 11 years ago

Hello, I want to get the end points of an Edge of a Graph. For example see the following source, In[1]:=gFriendShip = ExampleData[{"NetworkGraph", "Friendship"}]; In[2]:= EdgeList[gFriendShip, "Rose" \[UndirectedEdge] _] Out[2]:={"Anna" \[UndirectedEdge] "Rose", "Ben" \[UndirectedEdge] "Rose", "Rose" \[UndirectedEdge] "Nora"} Now I want to write something like EndPoints["Rose" \ "Nora"] (actually, EndPoints[%2] in above example) and want te get {"Rose", "Nora"} as output. It might be a basic thing but I am new to mathematica. Please help. Thank You.

POSTED BY: Suman Kundu

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Posted 11 years ago

List @@ # & /@ EdgeList[gFriendShip, "Rose" \[UndirectedEdge] _] returns {{"Anna", "Rose"}, {"Ben", "Rose"}, {"Rose", "Nora"}} Another perhaps more transparent pattern matching approch might be, EdgeList[gFriendShip, "Rose" \[UndirectedEdge] _] /. {x_ \[UndirectedEdge] y_ :> {x, y}} This is a 3 element list (rather than the 1 element list you suggested) because the EdgeList returns a 3 element list. If you only wanted cases where only {"Rose", "Nora"} is returned then you might use Select or Cases to get what you wish from the list above.

POSTED BY: David Reiss

Posted 11 years ago

The function Part can get into the parts of anything, not just lists: In[15]:= graph = Graph[{"Anna" \[UndirectedEdge] "Rose", "Ben" \[UndirectedEdge] "Rose", "Rose" \[UndirectedEdge] "Nora"}]; In[16]:= edges = EdgeList[graph] Out[16]= {"Anna" \[UndirectedEdge] "Rose", "Ben" \[UndirectedEdge] "Rose", "Rose" \[UndirectedEdge] "Nora"} In[17]:= edges[[1]] Out[17]= "Anna" \[UndirectedEdge] "Rose" In[18]:= edges[[1, 1]] Out[18]= "Anna" In[19]:= edges[[1, 2]] Out[19]= "Rose" In[20]:= edges[[All, {1, 2}]] Out[20]= {"Anna" \[UndirectedEdge] "Rose", "Ben" \[UndirectedEdge] "Rose", "Rose" \[UndirectedEdge] "Nora"}