Simplify

This example shows how to remove self loops and multiple edges using igraph.GraphBase.simplify().

import igraph as ig
import matplotlib.pyplot as plt

We start with a graph that includes loops and multiedges:

g1 = ig.Graph([
    (0, 1),
    (1, 2),
    (2, 3),
    (3, 4),
    (4, 0),
    (0, 0),
    (1, 4),
    (1, 4),
    (0, 2),
    (2, 4),
    (2, 4),
    (2, 4),
    (3, 3)],
)

To simplify the graph, we must remember that the function operates in place, i.e. directly changes the graph that it is run on. So we need to first make a copy of our graph, and then simplify that copy to keep the original graph untouched:

g2 = g1.copy()
g2.simplify()

<igraph.Graph object at 0x7fe83d4dd550>

We can then proceed to plot both graphs to see the difference. First, let’s choose a consistent visual style:

visual_style = {
    "vertex_color": "lightblue",
    "vertex_size": 20,
    "vertex_label": [0, 1, 2, 3, 4],
}

And finally, let’s plot them in twin axes, with rectangular frames around each plot:

fig, axs = plt.subplots(1, 2, sharex=True, sharey=True)
ig.plot(
    g1,
    layout="circle",
    target=axs[0],
    **visual_style,
)
ig.plot(
    g2,
    layout="circle",
    target=axs[1],
    **visual_style,
)
axs[0].set_title('Multigraph...')
axs[1].set_title('...simplified')
# Draw rectangles around axes
axs[0].add_patch(plt.Rectangle(
    (0, 0), 1, 1, fc='none', ec='k', lw=4, transform=axs[0].transAxes,
    ))
axs[1].add_patch(plt.Rectangle(
    (0, 0), 1, 1, fc='none', ec='k', lw=4, transform=axs[1].transAxes,
    ))
plt.show()