Interval Selection with Initial Date Range

This is an example of creating a stacked chart for which the domain of the top chart can be selected by interacting with the bottom chart. The initial selection range is set using Python’s native datetime objects.

Method syntax

import altair as alt
from vega_datasets import data
import datetime as dt

source = data.sp500.url

date_range = (dt.date(2007, 6, 30), dt.date(2009, 6, 30))

brush = alt.selection_interval(encodings=['x'],
                               value={'x': date_range})

base = alt.Chart(source, width=600, height=200).mark_area().encode(
    x = 'date:T',
    y = 'price:Q'
)

upper = base.encode(
    alt.X('date:T').scale(domain=brush)
)

lower = base.properties(
    height=60
).add_params(brush)

upper & lower

Attribute syntax

import altair as alt
from vega_datasets import data
import datetime as dt

source = data.sp500.url

date_range = (dt.date(2007, 6, 30), dt.date(2009, 6, 30))

brush = alt.selection_interval(encodings=['x'],
                               value={'x': date_range})

base = alt.Chart(source).mark_area().encode(
    x = 'date:T',
    y = 'price:Q'
).properties(
    width=600,
    height=200
)

upper = base.encode(
    alt.X('date:T', scale=alt.Scale(domain=brush))
)

lower = base.properties(
    height=60
).add_params(brush)

upper & lower