Adding parameters to altair chart crashes chart

Using Streamlit
1

image
image1099×701 84.6 KB

With the above dataset (both dates treated as strings), I am trying to create a heatmap chart altair. It needs to have interactivity, but when I add it via .add_params() the chart stops working, showing nothing at all.

Code:

selection_point = alt.selection_point(name="selected-point") 
heatmap = alt.Chart(heatmap_data).mark_rect().encode(
    x=alt.X('departureTime_Inbound:O', title='Inbound Date'),
    y=alt.Y('departureTime_Outbound:O', title='Outbound Date'),
    color=alt.Color('Number of Flights:Q', scale=alt.Scale(scheme='blues')),
    tooltip=['departureTime_Outbound', 'departureTime_Inbound', 'Number of Flights']
).properties(
    width=800,
    height=600,
    title="Flight Prices Heatmap"
).add_params(selection_point)

# Display the heatmap in Streamlit
data = st.altair_chart(heatmap, on_select="rerun")
st.write(data)

With selection parameter, the chart is as below

with params
with params1286×1359 28.3 KB

Without it (and without on_select argument on st.altair_chart())

without params
without params1310×1062 41.1 KB

2

Probably had to do with name="selected-point" attribute of the selection point. The dash seems to cause issues, solved by using an underscore.