Graph Element
In [1]:
import numpy as np
import pandas as pd
import holoviews as hv
import networkx as nx


The Graph element provides an easy way to represent and visualize network graphs. It differs from other elements in HoloViews in that it consists of multiple sub-elements. The data of the Graph element itself are the abstract edges between the nodes. By default the element will automatically compute concrete x and y positions for the nodes and represent them using a Nodes element, which is stored on the Graph. The abstract edges and concrete node positions are sufficient to render the Graph by drawing straight-line edges between the nodes. In order to supply explicit edge paths we can also declare EdgePaths , providing explicit coordinates for each edge to follow.

To summarize a Graph consists of three different components:

  • The Graph itself holds the abstract edges stored as a table of node indices.
  • The Nodes hold the concrete x and y positions of each node along with a node index . The Nodes may also define any number of value dimensions, which can be revealed when hovering over the nodes or to color the nodes by.
  • The EdgePaths can optionally be supplied to declare explicit node paths.

This reference document describes only basic functionality, for a more detailed summary on how to work with network graphs in HoloViews see the User Guide .

A simple Graph

Let's start by declaring a very simple graph connecting one node to all others. If we simply supply the abstract connectivity of the Graph , it will automatically compute a layout for the nodes using the layout_nodes operation, which defaults to a circular layout:

In [2]:
# Declare abstract edges
N = 8
node_indices = np.arange(N)
source = np.zeros(N)
target = node_indices

padding = dict(x=(-1.2, 1.2), y=(-1.2, 1.2))

simple_graph = hv.Graph(((source, target),)).redim.range(**padding)

Accessing the nodes and edges

We can easily access the Nodes and EdgePaths on the Graph element using the corresponding properties:

In [3]:
simple_graph.nodes + simple_graph.edgepaths

Additional features

Next we will extend this example by supplying explicit edges:

In [4]:
from matplotlib.colors import ListedColormap

# Node info
x, y = simple_graph.nodes.array([0, 1]).T
node_labels = ['Output']+['Input']*(N-1)

# Compute edge paths
def bezier(start, end, control, steps=np.linspace(0, 1, 100)):
    return (1-steps)**2*start + 2*(1-steps)*steps*control+steps**2*end

paths = []
for node_index in node_indices:
    ex, ey = x[node_index], y[node_index]
    paths.append(np.column_stack([bezier(x[0], ex, 0), bezier(y[0], ey, 0)]))

# Declare Graph
nodes = hv.Nodes((x, y, node_indices, node_labels), vdims='Type')
graph = hv.Graph(((source, target), nodes, paths))

                                  style=dict(cmap=ListedColormap(['blue', 'yellow'])))

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