Brtdku

I am using a selection dropdown in Bokeh to change what the chart shows. I'd also like the chart's legend to change accordingly. However, what happens instead is the legend becomes augmented every time the user selects a new dropdown value. Eventually, the legend displays every value from every possible dropdown option simultaneously. How do I "clear" the old legend on every new dropdown select?

import numpy as np

import pandas as pd

import os



from bokeh.plotting import figure

from bokeh.io import output_file, show, save, curdoc

from bokeh.models import HoverTool, CategoricalColorMapper, BoxSelectTool

from bokeh.models import ColumnDataSource, Select, Range1d

from bokeh.layouts import row, column, gridplot

from bokeh.models.widgets import Panel, Tabs

from bokeh.transform import factor_cmap



team = ['Bears', 'Bears', 'Bears', 'Bears', 'Bears']

player = ['Charles Leno', 'James Daniels', 'Cody Whitehair', 'Kyle Long', 'Bobby Massie']

position = ['LT', 'LG', 'C', 'RG', 'RT']

year_acquired = [2014, 2018, 2016, 2013, 2016]

round_drafted = [7, 2, 2, 1, np.NaN]

star=[False, False, False, True, False]



position_loc_x = [-4, -2, 0, 2, 4]

position_loc_y = [0, 0, 0, 0, 0]



year_acquired_color = ['green', 'yellow', 'blue', 'purple', 'blue']

round_drafted_color = ['grey', 'green', 'green', 'purple', np.NaN]

star_color = ['black', 'black', 'black', 'red', 'black']



df = pd.DataFrame({'team':team, 'player':player, 'position':position, 'year_acquired':year_acquired, 

                   'round_drafted':round_drafted, 'star':star, 'position_loc_x':position_loc_x, 

                   'position_loc_y':position_loc_y, 'year_acquired_color':year_acquired_color, 

                   'round_drafted_color':round_drafted_color, 'star_color':star_color})



p = figure(x_range=[-5,5], y_range=[-5, 5])



source = ColumnDataSource(data=df)



p.rect(source=source, x='position_loc_x', y=0, width=1, height=1, line_width=5, line_color=None,

       fill_color='round_drafted_color', legend='round_drafted')



hover = HoverTool(tooltips=[('Name', '@player'), ('Round', '@round_drafted'), ('Year', '@year_acquired')])

p.add_tools(hover)



def update():

    p.rect(source=source, x='position_loc_x', y=0, width=1, height=1, line_width=5, line_color=None, 

           fill_color=select.value, legend=select.value.rpartition('_')[0])



select = Select(title='choose an attribute', options=['round_drafted_color', 'year_acquired_color', 'star_color'], 

               value = 'round_drafted_color')



select.on_change('value', lambda attr, old, new: update())



p.legend.click_policy="hide"



layout = column(select, p)

curdoc().add_root(layout)

Instead of plotting the rectangle again with a new color/legendname, you should update the ColumnDataSource used to plot the rectangles. You can do this by editing the source.data dictionary.

#!/usr/bin/python3

import numpy as np

import pandas as pd

import os



from bokeh.plotting import figure

from bokeh.io import output_file, show, save, curdoc

from bokeh.models import HoverTool, CategoricalColorMapper, BoxSelectTool

from bokeh.models import ColumnDataSource, Select, Range1d

from bokeh.layouts import row, column, gridplot

from bokeh.models.widgets import Panel, Tabs

from bokeh.transform import factor_cmap



team = ['Bears', 'Bears', 'Bears', 'Bears', 'Bears']

player = ['Charles Leno', 'James Daniels', 'Cody Whitehair', 'Kyle Long', 'Bobby Massie']

position = ['LT', 'LG', 'C', 'RG', 'RT']

year_acquired = [2014, 2018, 2016, 2013, 2016]

round_drafted = [7, 2, 2, 1, np.NaN]

star=[False, False, False, True, False]



position_loc_x = [-4, -2, 0, 2, 4]

position_loc_y = [0, 0, 0, 0, 0]



year_acquired_color = ['green', 'yellow', 'blue', 'purple', 'blue']

round_drafted_color = ['grey', 'green', 'green', 'purple', np.NaN]

star_color = ['black', 'black', 'black', 'red', 'black']



df = pd.DataFrame({'team':team, 'player':player, 'position':position, 'year_acquired':year_acquired, 

                   'round_drafted':round_drafted, 'star':star, 'position_loc_x':position_loc_x, 

                   'position_loc_y':position_loc_y, 'year_acquired_color':year_acquired_color, 

                   'round_drafted_color':round_drafted_color, 'star_color':star_color, 'legend':round_drafted, 'color':round_drafted_color})



p = figure(x_range=[-5,5], y_range=[-5, 5])



source = ColumnDataSource(data=df)



glyph = p.rect(source=source, x='position_loc_x', y=0, width=1, height=1, line_width=5, line_color=None,

       fill_color='color', legend='legend')



hover = HoverTool(tooltips=[('Name', '@player'), ('Round', '@round_drafted'), ('Year', '@year_acquired')])

p.add_tools(hover)



def update():

    #Use select.value to get the right key from the dictionary and set its list as color/legend item

    source.data['color'] = source.data[select.value]

    source.data['legend'] = source.data[select.value.replace('_color', '')]





select = Select(title='choose an attribute', options=['round_drafted_color', 'year_acquired_color', 'star_color'], 

               value = 'round_drafted_color')



select.on_change('value', lambda attr, old, new: update())



p.legend.click_policy="hide"



layout = column(select, p)

curdoc().add_root(layout)