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#!/usr/bin/env python
"""
An example using networkx.XGraph().
miles_graph() returns an undirected graph over the 128 US cities from
the datafile miles.dat. The cities each have location and population
data. The edges are labeled with the distance betwen the two cities.
This example is described in Section 1.1 in Knuth's book [1,2].
References.
-----------
[1] Donald E. Knuth,
"The Stanford GraphBase: A Platform for Combinatorial Computing",
ACM Press, New York, 1993.
[2] http://www-cs-faculty.stanford.edu/~knuth/sgb.html
"""
__author__ = """Aric Hagberg (hagberg@lanl.gov)"""
# Copyright (C) 2004-2006 by
# Aric Hagberg <hagberg@lanl.gov>
# Dan Schult <dschult@colgate.edu>
# Pieter Swart <swart@lanl.gov>
# Distributed under the terms of the GNU Lesser General Public License
# http://www.gnu.org/copyleft/lesser.html
import networkx as NX
def miles_graph():
""" Return the cites example graph in miles.dat
from the Stanford GraphBase.
"""
try:
fh=open("miles.dat","r")
except IOError:
print "miles.dat not found"
raise
G=NX.XGraph()
G.position={}
G.population={}
cities=[]
for line in fh.readlines():
if line.startswith("*"): # skip comments
continue
numfind=re.compile("^\d+")
if numfind.match(line): # this line is distances
dist=line.split()
for d in dist:
G.add_edge(city,cities[i],int(d))
i=i+1
else: # this line is a city, position, population
i=1
(city,coordpop)=line.split("[")
cities.insert(0,city)
(coord,pop)=coordpop.split("]")
(y,x)=coord.split(",")
G.add_node(city)
# assign position - flip x axis for matplotlib, shift origin
G.position[city]=(-int(x)+7500,int(y)-3000)
G.population[city]=float(pop)/1000.0
return G
if __name__ == '__main__':
import networkx as NX
import re
import sys
G=miles_graph()
print "Loaded Donald Knuth's miles.dat containing 128 cities."
print "digraph has %d nodes with %d edges"\
%(NX.number_of_nodes(G),NX.number_of_edges(G))
# make new graph of cites, edge if less then 300 miles between them
H=NX.Graph()
for v in G:
H.add_node(v)
for (u,v,d) in G.edges():
if d < 300:
H.add_edge(u,v)
# draw with matplotlib/pylab
try:
import pylab as P
# with nodes sized py population
# draw(H,G.position,
# node_size=[G.population[v] for v in H],
# with_labels=False)
# with nodes colored by degree sized by population
node_color=P.array([float(H.degree(v)) for v in H])
NX.draw(H,G.position,
node_size=[G.population[v] for v in H],
node_color=node_color,
with_labels=False)
P.savefig("miles.png")
except:
pass
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