# Chord ¶

Title
Graph Element
Dependencies
Matplotlib
Backends
Matplotlib
Bokeh
In [1]:
import numpy as np
import pandas as pd
import holoviews as hv
from bokeh.sampledata.les_mis import data

hv.extension('matplotlib')
%output size=200 fig='svg'


The  Chord  element allows representing the inter-relationships between data points in a graph. The nodes are arranged radially around a circle with the relationships between the data points drawn as arcs (or chords) connecting the nodes. The number of chords is scaled by a weight declared as a value dimension on the  Chord  element.

If the weight values are integers, they define the number of chords to be drawn between the source and target nodes directly. If the weights are floating point values, they are normalized to a default of 500 chords, which are divided up among the edges. Any non-zero weight will be assigned at least one chord.

The  Chord  element is a type of  Graph  element and shares the same constructor. The most basic constructor accepts a columnar dataset of the source and target nodes and an optional value. Here we supply a dataframe containing the number of dialogues between characters of the Les Misérables musical. The data contains  source  and  target  node indices and an associated  value  column:

In [2]:
links = pd.DataFrame(data['links'])

   source  target  value
0       1       0      1
1       2       0      8
2       3       0     10


In the simplest case we can construct the  Chord  by passing it just the edges:

In [3]:
hv.Chord(links)

Out[3]:

To add node labels and other information we can construct a  Dataset  with a key dimension of node indices.

In [4]:
nodes = hv.Dataset(pd.DataFrame(data['nodes']), 'index')

Out[4]:
index group name
0 0 1 Myriel
1 1 1 Napoleon
2 2 1 Mlle.Baptistine
3 3 1 Mme.Magloire
4 4 1 CountessdeLo

Additionally we can now color the nodes and edges by their index and add some labels. The  label_index  ,  color_index  and  edge_color_index  allow specifying columns to color by.

In [5]:
%%opts Chord [label_index='name' color_index='index' edge_color_index='source']
%%opts Chord (cmap='Category20' edge_cmap='Category20')