Hi all,

gt allows creating graph views where vertices and/or edges are filtered out. The principle is described in the documentation:

"Vertices or edges which are to be filtered should be marked with a PropertyMap with value type bool, and then set with set_vertex_filter() or set_edge_filter() methods. By default, vertex or edges with value '1' are kept in the graphs, and those with value '0' are filtered out." (https://graph-tool.skewed.de/static/doc/quickstart.html#graph-filtering)

Given a layered graph, where layers are coded via an edge property, I want to draw the graphs layer by layer.

This is an example graph:

from graph_tool.all import *

import numpy as np

import pandas as pd

# data

edge_list = pd.DataFrame(np.array([[0, 1, 0], [1, 2, 1], [2, 0, 2]]), columns=['i', 'j', 'layer'])

# create graph

g = Graph(directed=False)

ep_layer = g.new_edge_property('int')

g.add_edge_list(edge_list.values, eprops=[ep_layer])

g.edge_properties['layer'] = ep_layer

# draw graph with edge colors showing the layers

graph_draw(g, edge_color=g.ep.layer)

It is possible to draw a single layer (in this example layer 0) in this complicated way:

# set layer to be drawn

layer = 0

# create graph view

ep_filter = g.new_edge_property('bool')

for i in range(0, len(edge_list)):

    e = g.edge(edge_list['i'][i], edge_list['j'][i])

    if edge_list['layer'][i] == layer:

ep_filter[e] = True

    else:

        ep_filter[e] = False

g_filter = GraphView(g, efilt=ep_filter)

# draw filtered graph

graph_draw(g_filter, edge_color=g.ep.layer)

If I proceed this way I will also have to create a vertex property map to filter unused vertices and do these steps for all layers I want to draw.

But isn’t there a more elegant way – preferably handling vertices and edges in the same step?

Many thanks and best wishes

Haiko