CODEWITHSUNDEEP
pythonnetworkx
Kristian Nielsen
Kristian Nielsen

Reputation: 149

Error when adding edges to network graph: 'v_of_edge'

I'm trying to create a network graph in NetworkX based on a defeaultdict which contains nodes and edges. When I try to add the edges, I get the following error message:

add_edge() missing 1 required positional argument: 'v_of_edge'

My code is as follows:

graph = { "a" : ["c"],
      "b" : ["c", "e"],
      "c" : ["a", "b", "d", "e"],
      "d" : ["c"],
      "e" : ["c", "b"],
      "f" : []
    } 

G = nx.Graph()

for k,v in graph.items():

    G.add_node(k)
    G.add_edge(*v)
nx.draw()
plt.show()

I know that add_edge takes (u,v) argument, where I suppose that u is node and v is the edges, so instead I tried:

G.add_edge(k,v)

But that resulted in a new error message saying:

unhashable type: 'list'

I don't know how to proceed, but it leaves me at least one question. In the second approach, should I somehow access each edge for a given node individually?

Upvotes: 3

Views: 8462

Answers (2)

YamiOmar88
YamiOmar88

Reputation: 1476

Here is a fix-up to your code that will make it work:

import networkx as nx
graph = {'a': ['c'], 'b': ['c', 'e'], 'c': ['a', 'b', 'd', 'e'], 'd': ['c'], 'e': ['c', 'b'], 'f': []}

G = nx.Graph()

for k,v in graph.items():
    G.add_node(k)
    for i in v:
        G.add_edge(k, i)

nx.draw(G)

import matplotlib.pyplot as plt
plt.show()

As you can see, the main issue is that you need to properly add each edge. Since your v are lists, you must go item by item in that list to add the edge.

Upvotes: 1

Yilun Zhang
Yilun Zhang

Reputation: 9008

The problem in your code is that v is a list in your graph structure definition. The following code will make it work:

graph = { "a" : ["c"],
      "b" : ["c", "e"],
      "c" : ["a", "b", "d", "e"],
      "d" : ["c"],
      "e" : ["c", "b"],
      "f" : []
    } 

G = nx.Graph()

for k,v in graph.items():
    for vv in v:
        G.add_edge(k,vv)
nx.draw(G)
plt.show()

Based on your definition, you are supposed to loop through the list associated with each node to define the edge.

enter image description here

Upvotes: 5

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