altair - Two titles with horizontally concatenated charts

Question

I'd like to concatenate two charts and then beautify the resulting combined chart (add some nice background). One important thing here is try to preserve titles for both charts.

When I try to do that, I either get the beautified combined chart with only one title or an error: ValueError: Objects with "background" attribute cannot be used within HConcatChart. Consider defining the background attribute in the HConcatChart object instead.

Here are some dummy code snippets of what I've tried.

Try #1 which yields only one title:

import altair as alt
from vega_datasets import data

source = data.cars()

line = alt.Chart(source).mark_line().encode(
    x='Year',
    y='mean(Miles_per_Gallon)'
)

band = alt.Chart(source).mark_errorband(extent='ci').encode(
    x='Year',
    y=alt.Y('Miles_per_Gallon', title='Miles/Gallon'),
)

combined = band | line
combined
combined.properties(background = '#f9f9f9',
                    title = alt.TitleParams(text = 'General title', 
                                            subtitle = ['Subtitle'],
                                            font = 'Ubuntu Mono', 
                                            fontSize = 22, 
                                            color = '#3E454F', 
                                            subtitleFont = 'Ubuntu Mono',
                                            subtitleFontSize = 16, 
                                            subtitleColor = '#3E454F')
                  )

Try #2 which yields a value error:

line2 = line.properties(background = '#f9f9f9',
                    title = alt.TitleParams(text = 'General title 1', 
                                            subtitle = ['Subtitle'],
                                            font = 'Ubuntu Mono', 
                                            fontSize = 22, 
                                            color = '#3E454F', 
                                            subtitleFont = 'Ubuntu Mono',
                                            subtitleFontSize = 16, 
                                            subtitleColor = '#3E454F')
                  )

band2 = band.properties(background = '#f9f9f9',
                    title = alt.TitleParams(text = 'General title 2', 
                                            subtitle = ['Subtitle'],
                                            font = 'Ubuntu Mono', 
                                            fontSize = 22, 
                                            color = '#3E454F', 
                                            subtitleFont = 'Ubuntu Mono',
                                            subtitleFontSize = 16, 
                                            subtitleColor = '#3E454F')
                  )
line2 | band2

Is there a way to achieve what I want? Or Altair doesn't allow this yet?

question from:https://stackoverflow.com/questions/65647305/two-titles-with-horizontally-concatenated-charts

Answer 1

You can specify the titles on the individual charts, and the background on the combined chart:

line2 = line.properties(
                    title = alt.TitleParams(text = 'General title 1', 
                                            subtitle = ['Subtitle'],
                                            font = 'Ubuntu Mono', 
                                            fontSize = 22, 
                                            color = '#3E454F', 
                                            subtitleFont = 'Ubuntu Mono',
                                            subtitleFontSize = 16, 
                                            subtitleColor = '#3E454F')
                  )

band2 = band.properties(
                    title = alt.TitleParams(text = 'General title 2', 
                                            subtitle = ['Subtitle'],
                                            font = 'Ubuntu Mono', 
                                            fontSize = 22, 
                                            color = '#3E454F', 
                                            subtitleFont = 'Ubuntu Mono',
                                            subtitleFontSize = 16, 
                                            subtitleColor = '#3E454F')
                  )

combined = band2 | line2
combined.properties(background = '#f9f9f9')