[BGL] python bindings build graph from edge list

1 Jun 2006

      Hi,

I was trying to build a graph from an edge list and ran into some 
problems. The following code throws an exception on write_graphviz(). I 
think it is because there's no property map called node_id in the graph.

import boost.graph as bgl
edges = [ ( 'a', 'b' ), ( 'b', 'c' ), ( 'c', 'a' ) ]
g = bgl.Graph( edges )
g.write_graphviz( 'bind-copy.dot' )

I get the following:
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
KeyError: 'node_id'

I couldn't manage to generate the node_id property map automatically. So 
after you have built the graph with the edge list constructor how do you 
know which vertex is which?

I ended up using the following code to create the graph:

def build( edges ):

	# Create a graph to build
	g = bgl.Graph()

	# Construct some property maps
	node_ids = g.vertex_properties[ 'node_id' ] = g.vertex_property_map( 
'string' )
	color = g.vertex_properties[ 'color' ] = g.vertex_property_map( 'string' )
	centrality = g.vertex_properties[ 'centrality' ] = 
g.vertex_property_map( 'float' )
	weight = g.edge_properties[ 'weight' ] = g.edge_property_map( 'float' )
	length = g.edge_properties[ 'len' ] = g.edge_property_map( 'float' )

	# create the edges and vertices
	name_2_vertex = { }
	for ( name1, name2 ) in edges:
		if not name_2_vertex.has_key( name1 ):
			v1 = name_2_vertex[ name1 ] = g.add_vertex()
			node_ids[ v1 ] = name1
		else:
			v1 = name_2_vertex[ name1 ]
		if not name_2_vertex.has_key( name2 ):
			v2 = name_2_vertex[ name2 ] = g.add_vertex()
			node_ids[ v2 ] = name2
		else:
			v2 = name_2_vertex[ name2 ]
		e = g.add_edge( v1, v2 )
		weight[ e ] = 0.1
		length[ e ] = 4

	# Color articulation points red
	for v in bgl.biconnected_components( g ):
		color[ v ] = 'red'

	# Assign centrality values to property map
	bgl.brandes_betweenness_centrality( g, centrality )

	return g

This code seems to works fine. So I thought I'd post this just to see if 
I was missing something obvious and/or in the hope someone else might 
find it useful.

Best,
John.

John Reid

Douglas Gregor

John Reid

Doug Gregor

John Reid

Douglas Gregor

John Reid

tags

participants (3)