Fading non-selected nodes and edges on Hover Chord diagram - Bokeh/Holoviews

I have been stuck at a problem for few days in customizing Holoviews Chord diagram. I have created a Chord diagram using some data set. When I hover on a node the node and it’s associated edges getting highlighted with some default color. But what I want is that when I hover on a node the node and it’s associated edges should get highlighted and also at the same time other non-selected nodes and edges should get faded away.

I am getting same effect on clicking on a node. But I want this feature on hover. I know it can be done using some javascript callback in Bokeh HoverTool but could not find a way to do it.

For example I want this on hover without clicking/tapping on node:

Adding source code for your reference:

source_data = [{"from": "Cronje", "to": "Lord Kitchener", "value": 1}, {"from": "Cronje", "to": "Lord Selborne", "value": 1}, {"from": "Cronje", "to": "George Godfrey", "value": 1}, {"from": "Cronje", "to": "Lord Milner", "value": 1}, {"from": "Cronje", "to": "Booker T. Washington", "value": 1}, {"from": "Cronje", "to": "Dada Abdulla", "value": 1}, {"from": "Cronje", "to": "Lord Lansdowne", "value": 1}, {"from": "Cronje", "to": "Escombe", "value": 1}, {"from": "Cronje", "to": "Messrs", "value": 1}, {"from": "Cronje", "to": "Lawley", "value": 1}, {"from": "Cronje", "to": "Sheth Haji Adam", "value": 1}, {"from": "Cronje", "to": "Lord Ripon", "value": 1}, {"from": "Cronje", "to": "Lord Elgin", "value": 1}, {"from": "Sheth Haji Adam", "to": "Lord Kitchener", "value": 1}, {"from": "Sheth Haji Adam", "to": "Lord Selborne", "value": 1}, {"from": "Sheth Haji Adam", "to": "George Godfrey", "value": 1}, {"from": "Sheth Haji Adam", "to": "Dada Abdulla", "value": 1}, {"from": "Sheth Haji Adam", "to": "Booker T. Washington", "value": 1}, {"from": "Sheth Haji Adam", "to": "Lord Milner", "value": 1}, {"from": "Sheth Haji Adam", "to": "Lord Lansdowne", "value": 1}, {"from": "Sheth Haji Adam", "to": "Escombe", "value": 1}, {"from": "Sheth Haji Adam", "to": "Messrs", "value": 1}, {"from": "Sheth Haji Adam", "to": "Lawley", "value": 1}, {"from": "Sheth Haji Adam", "to": "Lord Elgin", "value": 1}, {"from": "Sheth Haji Adam", "to": "Lord Ripon", "value": 1}, {"from": "Lord Selborne", "to": "Lord Elgin", "value": 1}, {"from": "Lord Selborne", "to": "George Godfrey", "value": 1}, {"from": "Lord Selborne", "to": "Merriman", "value": 1}, {"from": "Lord Selborne", "to": "Olive Schreiner", "value": 1}, {"from": "Lord Selborne", "to": "Dada Abdulla", "value": 1}, {"from": "Lord Selborne", "to": "Booker T. Washington", "value": 1}, {"from": "Lord Selborne", "to": "Lord Milner", "value": 1}, {"from": "Lord Selborne", "to": "Lord Kitchener", "value": 1}, {"from": "Lord Selborne", "to": "Lord Lansdowne", "value": 1}, {"from": "Lord Selborne", "to": "Escombe", "value": 1}, {"from": "Lord Selborne", "to": "Messrs", "value": 1}, {"from": "Lord Selborne", "to": "Lawley", "value": 1}, {"from": "Lord Selborne", "to": "John Molteno", "value": 1}, {"from": "Lord Selborne", "to": "Lord Ripon", "value": 1}, {"from": "George Godfrey", "to": "Dada Abdulla", "value": 1}, {"from": "George Godfrey", "to": "Booker T. Washington", "value": 1}, {"from": "George Godfrey", "to": "Lord Milner", "value": 1}, {"from": "George Godfrey", "to": "Lord Kitchener", "value": 1}, {"from": "George Godfrey", "to": "Lord Lansdowne", "value": 1}, {"from": "George Godfrey", "to": "Escombe", "value": 1}, {"from": "George Godfrey", "to": "Messrs", "value": 1}, {"from": "George Godfrey", "to": "Lawley", "value": 1}, {"from": "George Godfrey", "to": "Lord Elgin", "value": 1}, {"from": "George Godfrey", "to": "Lord Ripon", "value": 1}, {"from": "Merriman", "to": "Lord Lansdowne", "value": 1}, {"from": "Merriman", "to": "John Molteno", "value": 1}, {"from": "Merriman", "to": "Olive Schreiner", "value": 1}, {"from": "Olive Schreiner", "to": "Lord Lansdowne", "value": 1}, {"from": "Olive Schreiner", "to": "John Molteno", "value": 1}, {"from": "Dada Abdulla", "to": "Lord Kitchener", "value": 1}, {"from": "Dada Abdulla", "to": "Booker T. Washington", "value": 1}, {"from": "Dada Abdulla", "to": "Lord Milner", "value": 1}, {"from": "Dada Abdulla", "to": "Lord Lansdowne", "value": 1}, {"from": "Dada Abdulla", "to": "Escombe", "value": 1}, {"from": "Dada Abdulla", "to": "Messrs", "value": 1}, {"from": "Dada Abdulla", "to": "Lawley", "value": 1}, {"from": "Dada Abdulla", "to": "Lord Elgin", "value": 1}, {"from": "Dada Abdulla", "to": "Lord Ripon", "value": 1}, {"from": "Booker T. Washington", "to": "Lord Milner", "value": 1}, {"from": "Booker T. Washington", "to": "Lord Kitchener", "value": 1}, {"from": "Booker T. Washington", "to": "Lord Lansdowne", "value": 1}, {"from": "Booker T. Washington", "to": "Escombe", "value": 1}, {"from": "Booker T. Washington", "to": "Messrs", "value": 1}, {"from": "Booker T. Washington", "to": "Lawley", "value": 1}, {"from": "Booker T. Washington", "to": "Lord Elgin", "value": 1}, {"from": "Booker T. Washington", "to": "Lord Ripon", "value": 1}, {"from": "Lord Milner", "to": "Lord Kitchener", "value": 1}, {"from": "Lord Milner", "to": "Lord Lansdowne", "value": 1}, {"from": "Lord Milner", "to": "Escombe", "value": 1}, {"from": "Lord Milner", "to": "Messrs", "value": 1}, {"from": "Lord Milner", "to": "Lawley", "value": 1}, {"from": "Lord Milner", "to": "Lord Elgin", "value": 1}, {"from": "Lord Milner", "to": "Lord Ripon", "value": 1}, {"from": "Lord Kitchener", "to": "Lord Lansdowne", "value": 1}, {"from": "Lord Kitchener", "to": "Escombe", "value": 1}, {"from": "Lord Kitchener", "to": "Messrs", "value": 1}, {"from": "Lord Kitchener", "to": "Lawley", "value": 1}, {"from": "Lord Kitchener", "to": "Lord Elgin", "value": 1}, {"from": "Lord Kitchener", "to": "Lord Ripon", "value": 1}, {"from": "Lord Lansdowne", "to": "Escombe", "value": 1}, {"from": "Lord Lansdowne", "to": "Messrs", "value": 1}, {"from": "Lord Lansdowne", "to": "Lawley", "value": 1}, {"from": "Lord Lansdowne", "to": "John Molteno", "value": 1}, {"from": "Lord Lansdowne", "to": "Lord Elgin", "value": 1}, {"from": "Lord Lansdowne", "to": "Lord Ripon", "value": 1}, {"from": "Escombe", "to": "Messrs", "value": 1}, {"from": "Escombe", "to": "Lawley", "value": 1}, {"from": "Escombe", "to": "Lord Elgin", "value": 1}, {"from": "Escombe", "to": "Lord Ripon", "value": 1}, {"from": "Messrs", "to": "Lawley", "value": 1}, {"from": "Messrs", "to": "Lord Elgin", "value": 1}, {"from": "Messrs", "to": "Lord Ripon", "value": 1}, {"from": "Lawley", "to": "Lord Elgin", "value": 1}, {"from": "Lawley", "to": "Lord Ripon", "value": 1}, {"from": "Lord Elgin", "to": "Lord Ripon", "value": 1}]
        
        
import pandas as pd
import holoviews as hv
from holoviews import opts, dim
import numpy as np
hv.extension('bokeh')
hv.output(size=300)
        
        
df_json = pd.DataFrame(source_data)
        
df_links = pd.DataFrame(columns = ['source', 'target', 'value'])
        
df_links['source'] = df_json['from'].values.tolist()
df_links['target'] = df_json['to'].values.tolist()
df_links['value'] = df_json['value'].values.tolist()
        
unique_names = set(df_json['from'].unique().tolist() + df_json['to'].unique().tolist())
        
df_nodes = pd.DataFrame(columns=['name', 'group'])
df_nodes['name'] = list(unique_names)
        
## Grouping the nodes
df_nodes['group'][0:5] = 0
df_nodes['group'][5:10] = 1
df_nodes['group'][10:] = 2
        
## mapping to numerical value for the source and target node
mapper = {key: i for i, key in enumerate(list(unique_names))}
df_links['source'] = df_links['source'].map(mapper)
df_links['target'] = df_links['target'].map(mapper)
        
links = df_links
nodes = hv.Dataset(df_nodes, 'index')
        
chord = hv.Chord((links, nodes)).select(value=(1, None))
chord.opts(
      opts.Chord(cmap='Category10', edge_cmap='Category10', edge_color=dim('source').str(), 
                       labels='name', node_color=dim('group').str()))

Bokeh has the general ability to specify the appearance of hovered nodes and edges:

https://docs.bokeh.org/en/latest/docs/user_guide/graph.html#interaction-policies

But I am not sure how to apply this in the context of a HoloViews Chord diagram. That is probably a better question for the Holoviz Discourse.

Thanks for the quick response @Bryan . I will check it.
I am able to use HoverTool from bokeh.models inside my Holoviews Chord. More specifically is it possible to customize HoverTool such a way that satisfies my requirement? Any example code to customize HoverTool using customjs or anything would be really helpful.

@SAYANTAN_ADAK It’s not a matter of customizing the HoverTool. As shown in the link I provided, it is a matter of customizing the node and edge glyphs (i.e. how they react to being hovered). In your case it sounds like you want to also specify a nonselection_glyph to fade out things that are not hovered. But how to apply that to content created by Holoviews (instead of by hand as in the link) is something you will have to ask the holoviews support forum about.

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