使用选择区间与 mark_area

因为区域被视为一个对象，仅使用普通选择器将选择整个区域，而不是仅选择其中的一部分。

本示例展示了如何使用两个区域，一个在另一个之上，以及一个transform_filter来伪造这种效果。

Method syntax

import altair as alt
from vega_datasets import data

source = data.unemployment_across_industries.url

base = alt.Chart(source).mark_area(
    color='goldenrod',
    opacity=0.3
).encode(
    x='yearmonth(date):T',
    y='sum(count):Q',
)

brush = alt.selection_interval(encodings=['x'])
background = base.add_params(brush)
selected = base.transform_filter(brush).mark_area(color='goldenrod')

background + selected

Attribute syntax

import altair as alt
from vega_datasets import data

source = data.unemployment_across_industries.url

base = alt.Chart(source).mark_area(
    color='goldenrod',
    opacity=0.3
).encode(
    x='yearmonth(date):T',
    y='sum(count):Q',
)

brush = alt.selection_interval(encodings=['x'])
background = base.add_params(brush)
selected = base.transform_filter(brush).mark_area(color='goldenrod')

background + selected
# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.