code to plot some time series data with a vertical rule and hover box with the data point values

interactive_plot.py

data['Date'] = data['Date'].map(lambda d: f'{d}')
data = data.melt('Date')
# display(data)
line = altair.Chart(data).mark_line().encode(
    x=altair.X('Date:T', axis=altair.Axis(labelAngle=50, labelSeparation=10,
                                          format='%Y-%m-%d')),
    y=altair.Y('value', title=None, axis=altair.Axis(format='$,f')),
    color='variable',
)

# Create a selection that chooses the nearest point & selects based on
# x-value
nearest = altair.selection(type='single', nearest=True, on='mouseover',
                           fields=['Date'], empty='none')

# Transparent selectors across the chart. This is what tells us
# the x-value of the cursor
selectors = altair.Chart(data).mark_point().encode(
    x='Date:T',
    opacity=altair.value(0),
).add_selection(
    nearest
)

# Draw points on the line, and highlight based on selection
points = line.mark_point().encode(
    opacity=altair.condition(nearest, altair.value(1), altair.value(0))
)

# Draw text labels near the points, and highlight based on selection
text = line.mark_text(align='right', dx=-5, dy=-10).encode(
    text=altair.condition(
        nearest, 'value', altair.value(' '), format='$,d')
)

# Draw a rule at the location of the selection
rules = altair.Chart(data).mark_rule(color='gray').encode(
    x='Date',
).transform_filter(
    nearest
)

# Put the five layers into a chart and bind the data
return altair.layer(
    line, selectors, points, rules, text
).properties(
    width=1000, height=300
)