Node and Edge Labels

Labels

If the variables node_labels and edge_labels are set to True, the nodes and edges are labelled with the corresponding node and edge IDs. Alternatively, node_labels and edge_labels can be dictionaries that map node and edge IDs to custom strings.

Styling

The contents of the variables node_label_fontdict and edge_label_fontdict are passed to matplotlib.text.Text to stylise the node label and edge label text objects. Consult the matplotlib.text.Text documentation for a full list of available options. By default, the following values differ from the defaults for matplotlib.text.Text:

• size (adjusted to fit into node artists if no node_label_offset is used)

• horizontalalignment (default here: 'center')

• verticalalignment (default here: 'center')

• clip_on (default here: False)

• zorder (default here: inf)

Positioning

Edge labels are always centred on the corresponding edges. The position of the edge label along the edge can be controlled using the edge_label_position argument:

• 0.0 : edge labels are placed at the head of the edge

• 0.5 : edge labels are placed at the centre of the edge (default)

• 1.0 : edge labels are placed at the tail of the edge

If edge_label_rotate is True (default), edge labels are rotated such that they have the same orientation as their edge. If False, edge labels are not rotated; the angle of the text is parallel to the axis.

By default, node labels are centred on the corresponding nodes. However, they can also be offset using the node_label_offset parameter. If node_label_offset is a (float dx, float dy) tuple, node labels are offset by the corresponding amounts. If node_label_offset is a float, netgraph attempts to place node labels within that distance from node centres while avoiding collisions with node and edges.

import numpy as np
import matplotlib.pyplot as plt
import networkx as nx

from netgraph import Graph

fig, (ax1, ax2) = plt.subplots(1, 2)

triangle = [(0, 1), (0, 2), (1, 1), (1, 2), (2, 0)]

node_positions = {
    0 : np.array([0.2, 0.2]),
    1 : np.array([0.5, 0.8]),
    2 : np.array([0.8, 0.2]),
}

g = Graph(
    triangle,
    node_layout=node_positions, edge_layout='curved', edge_layout_kwargs=dict(k=0.025),
    node_labels={0 : 'a', 1 : 'b', 2 : 'c'},
    edge_labels=True, edge_label_fontdict=dict(fontweight='bold'),
    ax=ax1,
)

h = Graph(nx.complete_graph(7), edge_width=0.5, node_labels=True,
      node_label_fontdict=dict(size=14), node_label_offset=0.075, ax=ax2)

Node and edge label properties can also be changed individually after an initial draw using the standard matplotlib.text.Text methods:

# make changes
g.edge_label_artists[(0, 1)].set_style('italic')
g.node_label_artists[1].set_color('hotpink')

# force redraw to display changes
fig.canvas.draw()