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"""
Heat Lane Chart
---------------
This example shows how to make an alternative form of a histogram `designed at Google <https://www.smashingmagazine.com/2022/07/accessibility-first-approach-chart-visual-design/>`_ with the goal of increasing accessibility.
"""
# category: distributions
import altair as alt
from vega_datasets import data
source = data.cars.url
chart = alt.Chart(source, title="Car horsepower", height=100, width=300).encode(
x=alt.X(
"bin_Horsepower_start:Q",
title="Horsepower",
axis=alt.Axis(grid=False)
),
x2="bin_Horsepower_end:Q",
y=alt.Y("y:O", axis=None),
y2="y2",
).transform_bin(
["bin_Horsepower_start", "bin_Horsepower_end"],
field='Horsepower'
).transform_aggregate(
count='count()',
groupby=["bin_Horsepower_start", "bin_Horsepower_end"]
).transform_bin(
["bin_count_start", "bin_count_end"],
field='count'
).transform_calculate(
y="datum.bin_count_end/2",
y2="-datum.bin_count_end/2",
).transform_joinaggregate(
max_bin_count_end="max(bin_count_end)",
)
layer1 = chart.mark_bar(xOffset=1, x2Offset=-1, cornerRadius=3).encode(
color=alt.Color("max_bin_count_end:O", scale=alt.Scale(scheme="lighttealblue"), title="Number of models")
)
layer2 = chart.mark_bar(xOffset=1, x2Offset=-1, yOffset=-3, y2Offset=3).encode(
color=alt.Color("bin_count_end:O", title="Number of models")
)
layer1 + layer2
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