import streamlit as st
import pandas as pd
import numpy as np
import altair as alt
from vega_datasets import data
st.header("Demo placeholder altair chart")
cars = data.cars()
chart_placeholder = st.empty()

#interval = alt.selection_interval()

#c=alt.Chart(cars).mark_point().encode(
 #   x='Horsepower:Q',
  #  y='Miles_per_Gallon:Q',
   # color=alt.condition(interval, 'Origin', alt.value('lightgray'))
#).add_selection(
 #   interval
#)

single = alt.selection_single(on='mouseover', nearest=True)

c=alt.Chart(cars).mark_circle(size=100).encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color=alt.condition(single, 'Origin', alt.value('lightgray'))
).add_selection(
    single
)



#c = alt.Chart(cars).mark_point().encode(
 #   x='Horsepower:Q',
  #  y='Miles_per_Gallon:Q',
   # color='Origin',
    #tooltip='Name'
#).interactive()
chart_placeholder.altair_chart(c)