How do I highlight an entire trace upon hover in Plotly for Python?

Question

I want a trace to be highlighted (color or opacity change) when selected with mouse hover. I have looked into restyle functionality, but it may not be appropriate for my use case.

It looks like this has been discussed on Github, but I'm not sure if it has been resolved/implemented.

Here is an example in Bokeh of what I want to accomplish in Plotly Python:

from bokeh.plotting import figure, show, output_notebook
from bokeh.models import HoverTool
from bokeh.models import ColumnDataSource
output_notebook()

p = figure(plot_width=400, plot_height=400,y_range=(0.2,0.5))


y_vals = [0.22,0.22,0.25,0.25,0.26,0.26,0.27,0.27]
y_vals2 = [y*1.4 for y in y_vals]
x_vals = [0,1,1,2,2,2,2,3]
data_dict = {'x':[x_vals,x_vals],
             'y':[y_vals,y_vals2],
             'color':["firebrick", "navy"],
             'alpha':[0.1, 0.1]}

source = ColumnDataSource(data_dict)

p.multi_line('x','y',source=source,
             color='color', alpha='alpha', line_width=4,
             hover_line_alpha=1.0,hover_line_color='color')

p.add_tools(HoverTool(show_arrow=True,
                      line_policy='nearest',
                      ))
show(p)

Answer 1

You can use Plotly's FigureWidget functionality.

import plotly.graph_objs as go
import random

f = go.FigureWidget()
f.layout.hovermode = 'closest'
f.layout.hoverdistance = -1 #ensures no "gaps" for selecting sparse data
default_linewidth = 2
highlighted_linewidth_delta = 2

# just some traces with random data points  
num_of_traces = 5
random.seed = 42
for i in range(num_of_traces):
    y = [random.random() + i / 2 for _ in range(100)]
    trace = go.Scatter(y=y, mode='lines', line={ 'width': default_linewidth })
    f.add_trace(trace)

# our custom event handler
def update_trace(trace, points, selector):
    # this list stores the points which were clicked on
    # in all but one trace they are empty
    if len(points.point_inds) == 0:
        return
        
    for i,_ in enumerate(f.data):
        f.data[i]['line']['width'] = default_linewidth + highlighted_linewidth_delta * (i == points.trace_index)


# we need to add the on_click event to each trace separately       
for i in range( len(f.data) ):
    f.data[i].on_click(update_trace)

# let's show the figure 
f