"""
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." <http://ml.stat.purdue.edu/stat695t/writings/Trellis.User.pdf>`_. It became their favored way of showcasing the power of this pioneering plot.
"""
# category: case studies
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")
