Plotting networkx.Graph: how to change node position instead of resetting every node?

Question

I'm working on a project where I need to create a preview of nx.Graph() which allows to change position of nodes dragging them with a mouse. My current code is able to redraw whole figure immediately after each motion of mouse if it's clicked on specific node. However, this increases latency significantly. How can I update only artists needed, it is, clicked node, its label text and adjacent edges instead of refreshing every artist of plt.subplots()? Can I at least get a reference to all the artists that need to be relocated?

I started from a standard way of displaying a graph in networkx:

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

def refresh(G):
    plt.axis((-4, 4, -1, 3))
    nx.draw_networkx_labels(G, pos = nx.get_node_attributes(G, 'pos'),
                                bbox = dict(fc="lightgreen", ec="black", boxstyle="square", lw=3))
    nx.draw_networkx_edges(G, pos = nx.get_node_attributes(G, 'pos'), width=1.0, alpha=0.5)
    plt.show()

nodes = np.array(['A', 'B', 'C', 'D', 'E', 'F', 'G'])
edges = np.array([['A', 'B'], ['A', 'C'], ['B', 'D'], ['B', 'E'], ['C', 'F'], ['C', 'G']])
pos = np.array([[0, 0], [-2, 1], [2, 1], [-3, 2], [-1, 2], [1, 2], [3, 2]])

G = nx.Graph()
# IG = InteractiveGraph(G) #>>>>> add this line in the next step
G.add_nodes_from(nodes)
G.add_edges_from(edges)
nx.set_node_attributes(G, dict(zip(G.nodes(), pos.astype(float))), 'pos')

fig, ax = plt.subplots()
# fig.canvas.mpl_connect('button_press_event', lambda event: IG.on_press(event))
# fig.canvas.mpl_connect('motion_notify_event', lambda event: IG.on_motion(event))
# fig.canvas.mpl_connect('button_release_event', lambda event: IG.on_release(event))
refresh(G) # >>>>> replace it with IG.refresh() in the next step

In the next step I changed 5 line of previous script (4 is uncommented and 1 replaced) plus used InteractiveGraph instance to make it interactive:

class InteractiveGraph:
    def __init__(self, G, node_pressed=None, xydata=None):
        self.G = G
        self.node_pressed = node_pressed
        self.xydata = xydata

    def refresh(self, show=True):
        plt.clf()
        nx.draw_networkx_labels(self.G, pos = nx.get_node_attributes(self.G, 'pos'),
                                bbox = dict(fc="lightgreen", ec="black", boxstyle="square", lw=3))
        nx.draw_networkx_edges(self.G, pos = nx.get_node_attributes(self.G, 'pos'), width=1.0, alpha=0.5)
        plt.axis('off')
        plt.axis((-4, 4, -1, 3))
        fig.patch.set_facecolor('white')
        if show:
            plt.show()

    def on_press(self, event):
        if event.inaxes is not None and len(self.G.nodes()) > 0:
            nodelist, coords = zip(*nx.get_node_attributes(self.G, 'pos').items())
            kdtree = scipy.spatial.KDTree(coords)
            self.xydata = np.array([event.xdata, event.ydata])
            close_idx = kdtree.query_ball_point(self.xydata, np.sqrt(0.1))
            i = close_idx[0]
            self.node_pressed = nodelist[i]

    def on_motion(self, event):
        if event.inaxes is not None and self.node_pressed:
            new_xydata = np.array([event.xdata, event.ydata])
            self.xydata += new_xydata - self.xydata
            #print(d_xy, self.G.nodes[self.node_pressed])
            self.G.nodes[self.node_pressed]['pos'] = self.xydata
            self.refresh(show=False)
            event.canvas.draw()

    def on_release(self, event):
        self.node_pressed = None

Related sources:

• Event handling
• Optimized removal of closest node

Answer 1

To expand on my comment above, in netgraph, your example can be reproduced with

import numpy as np
import matplotlib.pyplot as plt; plt.ion()
import networkx as nx
import netgraph

nodes = np.array(['A', 'B', 'C', 'D', 'E', 'F', 'G'])
edges = np.array([['A', 'B'], ['A', 'C'], ['B', 'D'], ['B', 'E'], ['C', 'F'], ['C', 'G']])
pos = np.array([[0, 0], [-2, 1], [2, 1], [-3, 2], [-1, 2], [1, 2], [3, 2]])

G = nx.Graph()
G.add_nodes_from(nodes)
G.add_edges_from(edges)

I = netgraph.InteractiveGraph(G,
                              node_positions=dict(zip(nodes, pos)),
                              node_labels=dict(zip(nodes,nodes)),
                              node_label_bbox=dict(fc="lightgreen", ec="black", boxstyle="square", lw=3),
                              node_size=12,
)

# move stuff with mouse

---

Regarding the code you wrote, the kd-tree is unnecessary if you have handles of all the artists. In general, matplotlib artists have a contains method, such that when you log button press events, you can simply check artist.contains(event) to find out if the button press occurred over the artist. Of course, if you use networkx to do the plotting, you can't get the handles in a nice, query-able form (ax.get_children() is neither) so that is not possible.