# https://altair-viz.github.io/gallery/interactive_legend.html

import altair as alt
from vega_datasets import data

source = data.unemployment_across_industries.url

selection = alt.selection_multi(fields=["series"], bind="legend")

alt.Chart(source).mark_area().encode(
    alt.X("yearmonth(date):T", axis=alt.Axis(domain=False, format="%Y", tickSize=0)),
    alt.Y("sum(count):Q", stack="center", axis=None),
    alt.Color("series:N", scale=alt.Scale(scheme="category20b")),
    opacity=alt.condition(selection, alt.value(1), alt.value(0.2)),
).add_selection(selection)
