交互式平均值

下面的图表使用了区间选择，这使得图表包含一个交互式画刷（显示为灰色）。画刷选择参数化了红色的参考线，该参考线可视化了所选区间内的平均值。

方法语法

import altair as alt
from vega_datasets import data

source = data.seattle_weather()
brush = alt.selection_interval(encodings=['x'])

bars = alt.Chart().mark_bar().encode(
    x='month(date):O',
    y='mean(precipitation):Q',
    opacity = alt.when(brush).then(alt.value(1)).otherwise(alt.value(0.7)),
).add_params(
    brush
)

line = alt.Chart().mark_rule(color='firebrick').encode(
    y='mean(precipitation):Q',
    size=alt.SizeValue(3)
).transform_filter(
    brush
)

alt.layer(bars, line, data=source)

属性语法

import altair as alt
from vega_datasets import data

source = data.seattle_weather()
brush = alt.selection_interval(encodings=['x'])

bars = alt.Chart().mark_bar().encode(
    x='month(date):O',
    y='mean(precipitation):Q',
    opacity = alt.when(brush).then(alt.value(1)).otherwise(alt.value(0.7)),
).add_params(
    brush
)

line = alt.Chart().mark_rule(color='firebrick').encode(
    y='mean(precipitation):Q',
    size=alt.SizeValue(3)
).transform_filter(
    brush
)

alt.layer(bars, line, data=source)
# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.