title: Altair adding date slider for interactive scatter chart pot
body: <p>Has anyone tried using date as a slider for Altair interactive scatter plots? </p>
  
  <p>I'm trying to reproduce a similar plot to the gapminder scatter:
  1) Instead of a year filter I'm trying to use a date e.g. '2020-01-05' and having the follow error:</p>
  
  <pre><code>    altair.vegalite.v4.schema.core.BindRange-&gt;max, validating 'type'
  
      '2020-05-17T00:00:00' is not of type 'number'
  </code></pre>
  
  <p>2) When I try to parse it as an int, nothing shows up in the plot 
  3) Examples of using the Year slider: <a href="https://www.datacamp.com/community/tutorials/altair-in-python" rel="nofollow noreferrer">https://www.datacamp.com/community/tutorials/altair-in-python</a>
  <a href="https://altair-viz.github.io/gallery/multiple_interactions.html" rel="nofollow noreferrer">https://altair-viz.github.io/gallery/multiple_interactions.html</a>
  4) Also a timestamp option wouldn't be ideal as the date needs to be readable 
  Would appreciate any help. Thanks </p>
  
  <pre><code>#Date Slider
  from altair import datum
  from datetime import datetime
  import altair as alt
  import pandas as pd
  import numpy as np
  import datetime as dt
  
  date_slider = alt.binding_range(min=min(df['date']), max=max(df['date']), step=1)
  slider_selection = alt.selection_single(bind=date_slider, fields=['date'], name="Date", init={'week_starting': max(df[‘date’]})
  
  alt.Chart(df).mark_point(filled=True).encode(
      x='mom_pct',
      y='yoy_pct',
      size='n_queries',
      color='vertical',
      tooltip = ['vertical', 'yoy_pct', 'mom_pct']
  ).properties(
      width=800,
      height=600
  ).add_selection(slider_selection).transform_filter(slider_selection)
  </code></pre>