dataset = pd.read_csv('https://covid.ourworldindata.org/data/owid-covid-data.csv')
continents = dp.Params.get('continents', ['Asia', 'North America'])
field_to_plot = dp.Params.get('field_to_plot', 'new_cases_smoothed_per_million')
df = dataset[dataset.continent.isin(continents)].groupby(['continent', 'date'])[field_to_plot].mean().reset_index()
plot = alt.Chart(df).mark_area(opacity=0.4, stroke='black').encode(
y=alt.Y(field_to_plot, stack=None),
color=alt.Color('continent:N', scale=alt.Scale(scheme='set1')),
).interactive().properties(width='container')
).publish(name='covid_report', open=True)