Becker’s Barley Faceted Plot

The example demonstrates the faceted charts created by Richard Becker, William Cleveland and others in the 1990s. Using the visualization technique where each row is a different site (i.e. the chart is faceted by site), they identified an anomaly in a widely used agriculatural dataset, where the “Morris” site accidentally had the years 1931 and 1932 swapped. They named this “The Morris Mistake.”.

Method syntax

import altair as alt
from vega_datasets import data

source = data.barley()

alt.Chart(source, title="The Morris Mistake").mark_point().encode(
    alt.X('yield:Q')
        .title("Barley Yield (bushels/acre)")
        .scale(zero=False)
        .axis(grid=False),
    alt.Y('variety:N')
        .title("")
        .sort('-x')
        .axis(grid=True),
    alt.Color('year:N')
        .title("Year"),
    alt.Row('site:N')
        .title("")
        .sort(field='yield', op='sum', order='descending')
).properties(
    height=alt.Step(20)
).configure_view(stroke="transparent")

Attribute syntax

import altair as alt
from vega_datasets import data

source = data.barley()

alt.Chart(source, title="The Morris Mistake").mark_point().encode(
    alt.X(
        'yield:Q',
        title="Barley Yield (bushels/acre)",
        scale=alt.Scale(zero=False),
        axis=alt.Axis(grid=False)
    ),
    alt.Y(
        'variety:N',
        title="",
        sort='-x',
        axis=alt.Axis(grid=True)
    ),
    color=alt.Color('year:N', legend=alt.Legend(title="Year")),
    row=alt.Row(
        'site:N',
        title="",
        sort=alt.EncodingSortField(field='yield', op='sum', order='descending'),
    )
).properties(
    height=alt.Step(20)
).configure_view(stroke="transparent")