CODEWITHSUNDEEP
python-3.xnetworkx
Khali
Khali

Reputation: 21

KeyError: when using make_small_graph feature in networkx

I am trying to play around with graphs on from networkx. I'm coding in python and have the necessary extensions. The code block is:

gr = {"0": ["4"],
    "1": ["3"],
    "2": ["2", "3", "4", "5"],
    "3": ["1", "3"],
    "4": ["3"],
    "5": ["4"]
    }  
msg = nx.make_small_graph(gr)

but I receive this error:

Traceback (most recent call last):

File "C:\eclipse-workspace\graohToJSON\GraphToJSON.py", line 16, in 

msg = nx.make_small_graph(gr) #Make Small Graph

File "C:\AppData\Local\Programs\Python\Python37-32\lib\site-packages\networkx\generators\small.py", line 90, in make_small_graph

ltype = graph_description[0]

KeyError: 0

Upvotes: 0

Views: 496

Answers (2)

Joel
Joel

Reputation: 23827

I think Sparky05 has the best answer for you - namely that another command will handle the format you are trying to use (though I would recommend using ints instead of strings).

This answer explains what is wrong with the structure you've used.

From the documentation for make_small_graph:

make_small_graph(graph_description, create_using=None)

graph_description is a list of the form [ltype,name,n,xlist]

Here ltype is one of "adjacencylist" or "edgelist", name is the name of the graph and n the number of nodes. This constructs a graph of n nodes with integer labels 0,..,n-1.

If ltype="adjacencylist" then xlist is an adjacency list with exactly n entries, in with the j’th entry (which can be empty) specifies the nodes connected to vertex j.

... Use the create_using argument to choose the graph class/type.

So you've entered gr, which is a dict, whose keys are strings. But it is expecting something very different: a list for which gr[0] should either be "adjacencylist" or "edgelist", and whose other elements give other information about the graph.

So you need to make your input be a list, whose first element tells it the format of your information about the graph structure. Then the second element of your list needs to be a name you are giving your graph. The next element needs to be the number of nodes in your graph. The final entry needs to either be a list of edges or a list of lists giving the nodes adjacent to each node.

So as I understand your intent, you want a directed graph (otherwise 4 would have an edge also to 0, not just 0 having an edge to 4):

gr = ['adjacencylist', 'my_graph', 6, [[4], [3], [2,3,4,5], [1,3], [3], [4]]]

G = nx.make_small_graph(gr, create_using = nx.DiGraph)

There are several specific examples shown in the documentation, so take a look at them.

Upvotes: 1

Sparky05
Sparky05

Reputation: 4882

You can simply create the (directed?) graph directly:

import networkx as nx

gr = {"0": ["4"],
    "1": ["3"],
    "2": ["2", "3", "4", "5"],
    "3": ["1", "3"],
    "4": ["3"],
    "5": ["4"]
    }  
msg = nx.DiGraph(gr)
print(msg.edges)
# [('3', '3'), ('3', '1'), ('2', '4'), ('2', '3'), ('2', '2'), ('2', '5'), ('4', '3'), ('1', '3'), ('5', '4'), ('0', '4')]

Upvotes: 1

Related Questions