带滚动平均的条形图

一个叠加滚动平均的柱状图。在这个例子中，过去十年的值的平均值以一条线的形式显示。

Method syntax

import altair as alt
from vega_datasets import data

source = data.wheat()

bar = alt.Chart(source).mark_bar().encode(
    x='year:O',
    y='wheat:Q'
)

line = alt.Chart(source).mark_line(color='red').transform_window(
    # The field to average
    rolling_mean='mean(wheat)',
    # The number of values before and after the current value to include.
    frame=[-9, 0]
).encode(
    x='year:O',
    y='rolling_mean:Q'
)

(bar + line).properties(width=600)

Attribute syntax

import altair as alt
from vega_datasets import data

source = data.wheat()

bar = alt.Chart(source).mark_bar().encode(
    x='year:O',
    y='wheat:Q'
)

line = alt.Chart(source).mark_line(color='red').transform_window(
    # The field to average
    rolling_mean='mean(wheat)',
    # The number of values before and after the current value to include.
    frame=[-9, 0]
).encode(
    x='year:O',
    y='rolling_mean:Q'
)

(bar + line).properties(width=600)
# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.