Networkx and Plotly edges do not match

📊 Plotly Python
1

I’m trying to use Networkx 2.1 and Plotly 2.7.0 to generate a graph of a minimum spanning tree using a distance matrix as input. I am using Python 2.7.
The problem is that the edges of the nodes shown in the Plotly graph do not match the edgelist of the Networkx minimum spanning tree.
The distance matrix (csv file) has this format:

ST0_1,0,0,1109,1109,1091,1091,1125,1126,1126,1125,1127,1126,1127,1127,1125,1125,1125,1126,1126,1127,1127,1127,1127,1122,1130,1126,1127
    ST0_2,0,0,1109,1109,1091,1091,1125,1126,1126,1125,1127,1126,1127,1127,1125,1125,1125,1126,1126,1127,1127,1127,1127,1122,1130,1126,1127
    ST1_3,1109,1109,0,0,1107,1107,1047,1048,1048,1047,1049,1048,1049,1049,1049,1049,1049,1047,1049,1049,1047,1047,1047,1050,1050,1049,1049
    ST1_4,1109,1109,0,0,1107,1107,1047,1048,1048,1047,1049,1048,1049,1049,1049,1049,1049,1047,1049,1049,1047,1047,1047,1050,1050,1049,1049
    ST22_5,1091,1091,1107,1107,0,0,1100,1101,1101,1100,1102,1101,1102,1102,1101,1101,1101,1101,1100,1102,1101,1101,1102,1099,1103,1102,1102
    ST22_6,1091,1091,1107,1107,0,0,1100,1101,1101,1100,1102,1101,1102,1102,1101,1101,1101,1101,1100,1102,1101,1101,1102,1099,1103,1102,1102
    ST2,1125,1125,1047,1047,1100,1100,0,5,6,8,8,9,8,10,7,7,8,11,16,12,8,7,11,72,43,11,17
    ST7,1126,1126,1048,1048,1101,1101,5,0,1,7,3,4,3,5,6,6,7,10,15,13,7,6,10,72,43,6,16
    ST9,1126,1126,1048,1048,1101,1101,6,1,0,8,2,3,2,4,7,7,8,11,16,14,8,7,11,73,44,5,17
    ST5,1125,1125,1047,1047,1100,1100,8,7,8,0,10,11,10,12,7,7,8,7,16,16,10,9,13,73,44,13,17
    ST13,1127,1127,1049,1049,1102,1102,8,3,2,10,0,3,2,4,9,9,10,13,18,16,10,9,13,75,46,7,19
    ST11,1126,1126,1048,1048,1101,1101,9,4,3,11,3,0,3,1,10,10,11,14,19,17,11,10,14,76,47,8,20
    ST10,1127,1127,1049,1049,1102,1102,8,3,2,10,2,3,0,4,9,9,10,13,18,16,10,9,13,75,46,7,19
    ST12,1127,1127,1049,1049,1102,1102,10,5,4,12,4,1,4,0,11,11,12,15,20,18,12,11,15,77,48,9,21
    ST16_7,1125,1125,1049,1049,1101,1101,7,6,7,7,9,10,9,11,0,0,3,10,15,15,9,8,12,72,43,12,16
    ST16_8,1125,1125,1049,1049,1101,1101,7,6,7,7,9,10,9,11,0,0,3,10,15,15,9,8,12,72,43,12,16
    ST15,1125,1125,1049,1049,1101,1101,8,7,8,8,10,11,10,12,3,3,0,11,16,16,10,9,13,73,44,13,17
    ST6,1126,1126,1047,1047,1101,1101,11,10,11,7,13,14,13,15,10,10,11,0,17,15,11,12,12,70,43,14,18
    ST18,1126,1126,1049,1049,1100,1100,16,15,16,16,18,19,18,20,15,15,16,17,0,22,16,17,18,77,49,21,7
    ST17,1127,1127,1049,1049,1102,1102,12,13,14,16,16,17,16,18,15,15,16,15,22,0,14,15,15,75,50,15,23
    ST4,1127,1127,1047,1047,1101,1101,8,7,8,10,10,11,10,12,9,9,10,11,16,14,0,1,3,73,44,13,17
    ST3,1127,1127,1047,1047,1101,1101,7,6,7,9,9,10,9,11,8,8,9,12,17,15,1,0,4,74,45,12,18
    ST8,1127,1127,1047,1047,1102,1102,11,10,11,13,13,14,13,15,12,12,13,12,18,15,3,4,0,72,47,14,20
    ST21,1122,1122,1050,1050,1099,1099,72,72,73,73,75,76,75,77,72,72,73,70,77,75,73,74,72,0,83,74,79
    ST20,1130,1130,1050,1050,1103,1103,43,43,44,44,46,47,46,48,43,43,44,43,49,50,44,45,47,83,0,49,50
    ST14,1126,1126,1049,1049,1102,1102,11,6,5,13,7,8,7,9,12,12,13,14,21,15,13,12,14,74,49,0,22
    ST19,1127,1127,1049,1049,1102,1102,17,16,17,17,19,20,19,21,16,16,17,18,7,23,17,18,20,79,50,22,0

Here is the Python script:

import csv
    import numpy as np
    import networkx as nx
    from plotly.offline import plot
    import plotly.graph_objs as go
    from networkx.drawing.nx_agraph import graphviz_layout
    
    def read_dist_matrix(file_name):
        """ Reads a distance matrix in PHYLIP format.
       
            Requires: file_name is the name of a file that has the distance matrix
            in PHYLIP format.
            Ensures: distance matrix as numpy array and a list with the names/ids of
            each sequence.
        """
       
        with open(file_name) as f:
            #first_line = f.readline().strip()
            reader = csv.reader(f, delimiter=',')
            names = list(zip(*reader))[0]
    
        cols = tuple(list(range(1,len(names)+1)))
    
        dist_matrix = np.loadtxt(file_name, delimiter=',',
                                 usecols=cols)
    
        return [dist_matrix, names]
    
    
    def dist_to_graph(matrix, names):
        """ Converts numpy array representing distance matrix to graph.
       
            Requires: matrix as a numpy array. names as a list with the names
            of each row/column.
            Ensures: networkx graph labeled with the right names.
        """
       
        G = nx.from_numpy_matrix(matrix)
       
        nodes = list(G.nodes())
        
        names_dict = {}
        for n in range(len(nodes)):
            names_dict[nodes[n]] = names[n]
           
        G = nx.relabel_nodes(G, names_dict)
          
        return G
    
    ola = read_dist_matrix("out.csv")
    ola_g = dist_to_graph(ola[0], ola[1])

    mst = nx.minimum_spanning_tree(ola_g, algorithm='prim')
    pos = graphviz_layout(mst, prog='neato')
    labels = list(mst.nodes.keys())
    
    X = []
    Y = []
    
    for k in pos:
        X.append(pos[k][0])
        Y.append(pos[k][1])
        
    
    tracer = go.Scatter(x=X, y=Y,
                        mode='lines',
                        line=go.Line(color='#888', width=2),
                        hoverinfo = 'none',
                        showlegend=False)
                        
    tracer_marker = go.Scatter(x=X, y=Y,
                        mode='markers+text',
                        text=labels,
                        textposition='top',
                        marker = go.Marker(size= 15,
                                           line = dict(width = 2)),
                        hoverinfo = 'none',
                        showlegend=False)
                        
    layout = dict(title='Test', showlegend=False, 
                  xaxis=dict(title='', 
                             titlefont=dict(size=20), 
                             showgrid=False, 
                             zeroline=False, 
                             showline=False, 
                             ticks='', 
                             showticklabels=False, 
                             showspikes=False),
                  yaxis=dict(title='', 
                             titlefont=dict(size=20), 
                             showgrid=False, 
                             zeroline=False, 
                             showline=False, 
                             ticks='', 
                             showticklabels=False, 
                             showspikes=False)
                               )
    
    fig = dict(data=[tracer, tracer_marker], layout=layout)
    
    plot(fig, filename='./test_plotly.html', auto_open=True, show_link=False)

This is a screenshot of the output HTML:

output_html
output_html.png1233×733 64.8 KB

If we run the command mst.edges(data=True) we see that the nodes ST7 and ST5 are connected but in the Plotly graph they aren’t.

A similar question has been asked here, but it was on R:

Can anyone help me with this?

2

@xpotion
Your definition of edge trace does not assign the right coordinates to the edge ends.

I copied your csv file from the above post, saved it with the name data-spanning.csv, and modified your code such that Plotly can now generate the right graph.

Here is the updated code: https://plot.ly/~empet/14899

minim-spanning-tree
minim-spanning-tree.png800×600 25.1 KB

3

Thank you very much @empet, the problem is solved!

4

@empet sorry to bring this up now but what the N=len(coords) line does in the code you sent?

I’ve been using the code you wrote but only now I’ve noticed that this line is, apparently, not doing anything.

5

@xpotion You are right. N=len(coords) is not necessary. I pasted there a function that I used to get Plotly data, but the graph nodes were V=range(N), not strings as in your case. I modified the code to be adequate for nodes as strings and I forgot to delete that line.

Now I noticed that node_label is used as a global variable. Please define

def get_plotly_data(E, coords, node_label):
6

Thanks once again @empet! I will change the code accordingly.