Get the End Points of an Edge

Questions
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1

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.

2

Cross-posted: http://mathematica.stackexchange.com/questions/45355

3

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"}
4 
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.