0

I people, I'm trying to plot a network graph using networkx module, but I am having results I was not expecting and I am starting to ask myself if it is any module issue!

I have this code inside a class:

def plotGraph(self):
    conn = []
    nodeLabel = {}

    for node_idx in self.operatorNodes:
        print("i = ", node_idx)
        print(self.node[node_idx].childs)
        for child in self.node[node_idx].childs:
            conn.append((child.idx, node_idx))

    for i in range(self.nn):
        nodeLabel[i] = str(i) + ": " + self.node[i].opString

    node_color = ['blue'] * self.nn
    #for i in range(self.nOutputs):
    #    node_color[i] = 'red'

    node_color[0] = 'red'

    print('Graph Conn = ', conn)
    print('Graph Color = ', node_color)
    # you may name your edge labels
    labels = map(chr, range(65, 65 + len(conn)))
    print('nodeLabel = ', nodeLabel)

    draw_graph(conn, nodeLabel, node_color=node_color, labels=labels)

From the prints I can see that what is being passed inside the draw_graph is (draw_graph code is based in https://www.udacity.com/wiki/creating-network-graphs-with-python):

Graph Conn =  [(2, 0), (3, 0), (4, 1), (5, 1), (6, 2), (7, 2), (8, 5), (9, 5)]
Graph Color =  ['red', 'blue', 'blue', 'blue', 'blue', 'blue', 'blue', 'blue', 'blue', 'blue']
nodeLabel =  {0: '0: mul', 1: '1: mul', 2: '2: mul', 3: '3: cte', 4: '4: cte', 5: '5: sum', 6: '6: cte', 7: '7: cte', 8: '8: cte', 9: '9: cte'}

Yet the plot is the following

draw_graph code is:

def draw_graph(graph, nodeLabel, node_color, labels=None, graph_layout='shell',
               node_size=1600, node_alpha=0.3,
               node_text_size=12,
               edge_color='blue', edge_alpha=0.3, edge_tickness=1,
               edge_text_pos=0.3,
               text_font='sans-serif'):

    # create networkx graph
    G=nx.DiGraph()

    # add edges
    for edge in graph:
        G.add_edge(edge[0], edge[1])

    # these are different layouts for the network you may try
    # shell seems to work best
    if graph_layout == 'spring':
        graph_pos = nx.spring_layout(G)
    elif graph_layout == 'spectral':
        graph_pos = nx.spectral_layout(G)
    elif graph_layout == 'random':
        graph_pos = nx.random_layout(G)
    else:
        graph_pos = nx.shell_layout(G)

    # draw graph
    nx.draw_networkx_edges(G, graph_pos, width=edge_tickness, alpha=edge_alpha, edge_color=edge_color)
    nx.draw_networkx_labels(G, graph_pos, labels=nodeLabel, font_size=node_text_size, font_family=text_font)

    if labels is None:
        labels = range(len(graph))

    edge_labels = dict(zip(graph, labels))
    nx.draw_networkx_edge_labels(G, graph_pos, edge_labels=edge_labels, label_pos=edge_text_pos)

    nx.draw(G, graph_pos, node_size=node_size, alpha=node_alpha, node_color=node_color)

Has can be seen, the Graph Color in 0 position is red and the remain should be blue, yet the plot is putting in the third node! There is no way for me to access node 1 has well, apparently, nodes are misplaced! The nodes color are placed in the following positions [2, 0, 3, 4, 5,....].

Sergio Cavaleiro Costa
  • 529
  • 1
  • 4
  • 15

1 Answers1

2

When you use nx.draw and pass it an (optional) list of colors, it will assign those colors to the nodes in the same order as the (optional) nodelist. But you didn't define nodelist. So it will default to whatever order comes out of G.nodes().

Since the underlying data structure for a networkx graph is a dictionary, you have to deal with the fact that you cannot count on the nodes to have any specified order.

Try passing nodelist into the nx.draw command in the order you want.

Joel
  • 22,598
  • 6
  • 69
  • 93