title: Multiple Transform Filters, Altair
body: <p>Is there any way in which to get say three charts working together, where a selection on any one of them updates the other?</p>
  
  <p>This only seems possible for two plots, since from what I can see, you can only attach one transform filter.</p>
  
  <p>e.g. </p>
  
  <pre><code>brush = alt.selection(type='interval')
  nationality_select = alt.selection(type='single', fields=['Nationality'])
  club_select = alt.selection(type='single', fields=['Club_Position'])
  
  points = alt.Chart().mark_circle().encode(
  x='Acceleration',
  y='Speed',
  color=alt.condition(brush, 'Nationality:N', alt.value('lightgray')),
  tooltip=['Club_Position', 'Name']
  ).add_selection(
      brush
  ).transform_filter(
      nationality_select
  )
  
  bars_nationality = alt.Chart().mark_bar().encode(
      color='Nationality',
      x='count(Nationality)',
      y=alt.Y('Nationality',
          sort=alt.SortField(field='count', order='descending', op='max')
      )
  ).properties(
      selection=nationality_select
  ).transform_filter(
      brush
  )
  
  bars_club_position = alt.Chart().mark_bar().encode(
      color='Club_Position',
      x='count(Club_Position)',
      y=alt.Y('Club_Position',
      sort=alt.SortField(field='count', order='descending', op='max')
      )
  ).properties(
      selection=club_select
  ).transform_filter(
      brush
  )
  
  alt.vconcat(points, bars_nationality, bars_club_position, d 
  data=fifa.sample(2000))
  </code></pre>
  
  <p>I can't do this for example</p>
  
  <pre><code>.transform_filter(
      brush, nationality_filter
  )
  </code></pre>
  
  <p>So is there any way in which to add multiple?</p>