Update dynamically colorbar title - Plotly

Question

I'm trying to update the colorbar title based on the button selection, wihtout success so far.

Here is my code :

import numpy as np
import plotly.graph_objects as go

df = pd.DataFrame(np.array([['Germany', 2, 3], ['United States', 5, 6], ["Italy", 8, 9]]),
                   columns=['country', 'data_a', 'data_b'])

fig = go.Figure(data=go.Choropleth(
    locations = df['country'],
    z = df['data_a'],
    text = df['country'],
    colorscale = 'Teal',
    autocolorscale=False,
    reversescale=False,
    marker_line_color='black',
    marker_line_width=0.3,
    colorbar_title = '<b>data_a_title</b>',
    locationmode ='country names'
))

#update map style
fig.update_layout(
    geo=dict(
        showframe=False,
        showcoastlines=True,
        projection_type='equirectangular'
    )
)
 

#dropdown menu
button1 =  dict(method = "update",
                args = [{'z': [ df["data_a"] ] },
                       {"colorbar":{"title":"data_a_title"}}],
                label = "data_a")
button2 =  dict(method = "update",
                args = [{'z': [ df["data_b"] ]},
                       {"colorbar_title":'data_b_title'}],
                label = "data_b")


fig.update_layout(width=700,
                  coloraxis_colorbar_thickness=23,
                  updatemenus=[dict(y=0.2,
                                    x=1,
                                    xanchor='right',
                                    yanchor='bottom',
                                    active=0,
                                    buttons=[button1, button2])
                              ]) 

fig.show(config={"displayModeBar": False, "showTips": False})

As you can see, I tried with this : {"colorbar":{"title":"data_a_title"}}

or {"colorbar_title":'data_b_title'}

but none of them worked. Any idea about what I'm missing ?

Thank you!

Answer 1

for a chorpeth the colorbar title is part of the trace, not the layout. Hence your button definitions become:

#dropdown menu
button1 =  dict(method = "update",
                args = [{'z': [ df["data_a"] ], "colorbar":{"title":{"text":"data_a_title"} }},
                       {}],
                label = "data_a")
button2 =  dict(method = "update",
                args = [{'z': [ df["data_b"] ], "colorbar":{"title":{"text":"data_b_title"} }},

                       {}],
                label = "data_b")

Simplest way to understand this is to look at fig.data and fig.layout to understand the structure of the figure