# https://altair-viz.github.io/gallery/density_facet.html
import altair as alt
from vega_datasets import data

source = data.iris()

alt.Chart(source).transform_fold(
    ["petalWidth", "petalLength", "sepalWidth", "sepalLength"],
    as_=["Measurement_type", "value"],
).transform_density(
    density="value", bandwidth=0.3, groupby=["Measurement_type"], extent=[0, 8]
).mark_area().encode(
    alt.X("value:Q"), alt.Y("density:Q"), alt.Row("Measurement_type:N")
).properties(width=300, height=50)
