Becker’s Barley Trellis Plot

The example demonstrates the trellis charts created by Richard Becker, William Cleveland and others in the 1990s. Using the visualization technique below they identified an anomoly in a widely used agriculatural dataset, which they termed “The Morris Mistake.”. It became their favored way of showcasing the power of this pioneering plot.

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')
        .legend(title="Year"),
    alt.Row('site:N')
        .title("")
        .sort(alt.EncodingSortField(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")