Node positioning algorithms for graph drawing.
"""
Copyright (C) 2004-2015 by
Aric Hagberg hagberg@lanl.gov
Dan Schult dschult@colgate.edu
Pieter Swart swart@lanl.gov
All rights reserved.
BSD license.
import collections
import networkx as nx
author = """Aric Hagberg (hagberg@lanl.gov)nDan Schult(dschult@colgate.edu)"""
all = ['circular_layout','random_layout','shell_layout','spring_layout','spectral_layout','fruchterman_reingold_layout']
def process_params(G,center,dim):
Some boilerplate code.
import numpy as np
if not isinstance(G,nx.Graph):
empty_graph = nx.Graph()
empty_graph.add_nodes_from(G)
G = empty_graph
if center is None:
center = np.zeros(dim)
else:
center = np.asarray(center)
if len(center) != dim:
msg = "length of center coordinates must match dimension of layout"
raise ValueError(msg)
return G,center
[docs]def random_layout(G,dim=2,center=None):
"""Position nodes uniformly at random in the unit square.
For every node,a position is generated by choosing each of dim
coordinates uniformly at random on the interval [0.0,1.0).
NumPy (http://scipy.org) is required for this function.
Parameters
----------
G : NetworkX graph or list of nodes
A position will be assigned to every node in G.
dim : int
Dimension of layout.
center : array-like or None
Coordinate pair around which to center the layout.
Returns
-------
pos : dict
A dictionary of positions keyed by node
Examples
--------
>>> G = nx.lollipop_graph(4,3)
>>> pos = nx.random_layout(G)
"""
import numpy as np
G,center = process_params(G,dim)
shape = (len(G),dim)
pos = np.random.random(shape) + center
pos = pos.astype(np.float32)
pos = dict(zip(G,pos))
return pos
[docs]def circular_layout(G,scale=1,center=None):
dim=2 only
"""Position nodes on a circle.
Parameters
----------
G : NetworkX graph or list of nodes
dim : int
Dimension of layout,currently only dim=2 is supported
scale : float
Scale factor for positions
center : array-like or None
Coordinate pair around which to center the layout.
Returns
-------
dict :
A dictionary of positions keyed by node
Examples
--------
>>> G=nx.path_graph(4)
>>> pos=nx.circular_layout(G)
Notes
------
This algorithm currently only works in two dimensions and does not
try to minimize edge crossings.
"""
import numpy as np
G,dim)
if len(G) == 0:
pos = {}
elif len(G) == 1:
pos = {G.nodes()[0]: center}
else:
# Discard the extra angle since it matches 0 radians.
theta = np.linspace(0,1,len(G) + 1)[:-1] * 2 * np.pi
theta = theta.astype(np.float32)
pos = np.column_stack([np.cos(theta),np.sin(theta)])
pos = _rescale_layout(pos,scale=scale) + center
pos = dict(zip(G,pos))
return pos
[docs]def shell_layout(G,nlist=None,center=None):
"""Position nodes in concentric circles.
Parameters
----------
G : NetworkX graph or list of nodes
nlist : list of lists
List of node lists for each shell.
dim : int
Dimension of layout,currently only dim=2 is supported
scale : float
Scale factor for positions
center : array-like or None
Coordinate pair around which to center the layout.
Returns
-------
dict :
A dictionary of positions keyed by node
Examples
--------
>>> G = nx.path_graph(4)
>>> shells = [[0],[1,2,3]]
>>> pos = nx.shell_layout(G,shells)
Notes
------
This algorithm currently only works in two dimensions and does not
try to minimize edge crossings.
"""
import numpy as np
G,dim)
if len(G) == 0:
return {}
elif len(G) == 1:
return {G.nodes()[0]: center}
if nlist is None:
# draw the whole graph in one shell
nlist = [list(G.nodes())]
if len(nlist[0]) == 1:
# single node at center
radius = 0.0
else:
# else start at r=1
radius = 1.0
npos={}
for nodes in nlist:
# Discard the extra angle since it matches 0 radians.
theta = np.linspace(0,len(nodes) + 1)[:-1] * 2 * np.pi
theta = theta.astype(np.float32)
pos = np.column_stack([np.cos(theta),scale=scale * radius / len(nlist)) + center
npos.update(zip(nodes,pos))
radius += 1.0
return npos
def fruchterman_reingold_layout(G,k=None,pos=None,fixed=None,iterations=50,weight='weight',scale=1.0,center=None):
"""Position nodes using Fruchterman-Reingold force-directed algorithm.
Parameters
----------
G : NetworkX graph or list of nodes
dim : int
Dimension of layout
k : float (default=None)
Optimal distance between nodes. If None the distance is set to
1/sqrt(n) where n is the number of nodes. Increase this value
to move nodes farther apart.
pos : dict or None optional (default=None)
Initial positions for nodes as a dictionary with node as keys
and values as a list or tuple. If None,then use random initial
positions.
fixed : list or None optional (default=None)
Nodes to keep fixed at initial position.
iterations : int optional (default=50)
Number of iterations of spring-force relaxation
weight : string or None optional (default='weight')
The edge attribute that holds the numerical value used for
the edge weight. If None,then all edge weights are 1.
scale : float (default=1.0)
Scale factor for positions. The nodes are positioned
in a box of size [0,scale] x [0,scale].
center : array-like or None
Coordinate pair around which to center the layout.
Returns
-------
dict :
A dictionary of positions keyed by node
Examples
--------
>>> G=nx.path_graph(4)
>>> pos=nx.spring_layout(G)
# The same using longer function name
>>> pos=nx.fruchterman_reingold_layout(G)
"""
import numpy as np
G,dim)
if fixed is not None:
nfixed = dict(zip(G,range(len(G))))
fixed = np.asarray([nfixed[v] for v in fixed])
if pos is not None:
# Determine size of existing domain to adjust initial positions
dom_size = max(flatten(pos.values()))
shape = (len(G),dim)
pos_arr = np.random.random(shape) * dom_size + center
for i,n in enumerate(G):
if n in pos:
pos_arr[i] = np.asarray(pos[n])
else:
pos_arr=None
if len(G) == 0:
return {}
if len(G) == 1:
return {G.nodes()[0]: center}
try:
# Sparse matrix
if len(G) < 500: # sparse solver for large graphs
raise ValueError
A = nx.to_scipy_sparse_matrix(G,weight=weight,dtype='f')
if k is None and fixed is not None:
# We must adjust k by domain size for layouts that are not near 1x1
nnodes,_ = A.shape
k = dom_size / np.sqrt(nnodes)
pos = _sparse_fruchterman_reingold(A,dim,k,pos_arr,fixed,iterations)
except:
A = nx.to_numpy_matrix(G,weight=weight)
if k is None and fixed is not None:
# We must adjust k by domain size for layouts that are not near 1x1
nnodes,_ = A.shape
k = dom_size / np.sqrt(nnodes)
pos = _fruchterman_reingold(A,iterations)
if fixed is None:
pos = _rescale_layout(pos,scale=scale) + center
pos = dict(zip(G,pos))
return pos
spring_layout=fruchterman_reingold_layout
def _fruchterman_reingold(A,iterations=50):
Position nodes in adjacency matrix A using Fruchterman-Reingold
# Entry point for NetworkX graph is fruchterman_reingold_layout()
try:
import numpy as np
except ImportError:
raise ImportError("_fruchterman_reingold() requires numpy: http://scipy.org/ ")
try:
nnodes,_=A.shape
except AttributeError:
raise nx.NetworkXError(
"fruchterman_reingold() takes an adjacency matrix as input")
A=np.asarray(A) # make sure we have an array instead of a matrix
if pos==None:
# random initial positions
pos=np.asarray(np.random.random((nnodes,dim)),dtype=A.dtype)
else:
# make sure positions are of same type as matrix
pos=pos.astype(A.dtype)
# optimal distance between nodes
if k is None:
k=np.sqrt(1.0/nnodes)
# the initial "temperature" is about .1 of domain area (=1x1)
# this is the largest step allowed in the dynamics.
# We need to calculate this in case our fixed positions force our domain
# to be much bigger than 1x1
t = max(max(pos.T[0]) - min(pos.T[0]),max(pos.T[1]) - min(pos.T[1]))*0.1
# simple cooling scheme.
# linearly step down by dt on each iteration so last iteration is size dt.
dt=t/float(iterations+1)
delta = np.zeros((pos.shape[0],pos.shape[0],pos.shape[1]),dtype=A.dtype)
# the inscrutable (but fast) version
# this is still O(V^2)
# could use multilevel methods to speed this up significantly
for iteration in range(iterations):
# matrix of difference between points
for i in range(pos.shape[1]):
delta[:,:,i]= pos[:,i,None]-pos[:,i]
# distance between points
distance=np.sqrt((delta**2).sum(axis=-1))
# enforce minimum distance of 0.01
distance=np.where(distance<0.01,0.01,distance)
# displacement "force"
displacement=np.transpose(np.transpose(delta)*
(k*k/distance**2-A*distance/k))
.sum(axis=1)
# update positions
length=np.sqrt((displacement**2).sum(axis=1))
length=np.where(length<0.01,0.1,length)
delta_pos=np.transpose(np.transpose(displacement)*t/length)
if fixed is not None:
# don't change positions of fixed nodes
delta_pos[fixed]=0.0
pos+=delta_pos
# cool temperature
t-=dt
return pos
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