Bar Chart with Line at Mean

This example shows the mean value overlayed on a bar chart.

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'
)

rule = alt.Chart(source).mark_rule(color='red').encode(
    y='mean(wheat):Q'
)

(bar + rule).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'
)

rule = alt.Chart(source).mark_rule(color='red').encode(
    y='mean(wheat):Q'
)

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