Bokeh: [BUG] Jitter caching too aggressively

Created on 4 Dec 2020 · 3Comments · Source: bokeh/bokeh

Versions

bokeh 2.2.3 (via conda 4.8.3); Mac OS X 10.15.7

Description of expected behavior and the observed behavior

Scatter points jittered on a categorical axis don't move when the categorical factor range (provided as range parameter) is modified. In a Discourse thread, Bryan put this down to a "deficiency in the current caching behavior of the jitter transform".

Below is a brief example where a button reverses a categorical axis: red jittered points move, blue jittered ones don’t.

Example

from bokeh.transform import jitter
from bokeh.models import ColumnDataSource, FactorRange, CustomJS
from bokeh.models.widgets import Button
from bokeh.layouts import column
from bokeh.plotting import figure
from bokeh.io import show

source = ColumnDataSource({
    'name': ['a', 'a', 'a', 'a', 'a'],
    'val': [1, 1, 1, 1, 1],
})

p = figure(x_range=FactorRange(factors=['a', 'b']),  
           y_range=(0, 2), plot_width=200, plot_height=200)

p.scatter(x=jitter('name', 0.5, range=p.x_range), y='val', size=5, alpha=0.5, color='blue', source=source)
p.scatter(x='name', y=jitter('val', 0.5), size=5, color='red', alpha=0.5, source=source)

button = Button(label='Reorder factors')
button.js_on_click(CustomJS(args={'x_range': p.x_range}, code="""
    const factors = [...x_range.factors];
    const reversed = factors.reverse();
    x_range.factors = reversed;
"""))
column = column(button, p)
show(column)