title: cross-filtering with different chart encodings via `hconcat` and `layer`
body: <p>I was trying to adapt the <a href="https://vega.github.io/vega-lite/examples/interactive_layered_crossfilter.html" rel="nofollow noreferrer">cross-filter example from the gallary</a> to have an additional chart that is not a numeric value, e.g., <code>origin</code> from the <a href="https://vega.github.io/editor/data/flights-2k.json" rel="nofollow noreferrer">flights data set in the same example</a>. However, the selections became rather strange after I moved the <code>transform</code> into the <code>hconcat</code> layer---opening a new chart instead of updating in place. I also wasn't sure how the selections composed across the charts now that there is another level of composition (<code>hconcat</code> in additional to <code>repeat</code> layering).</p>
  
  <p><a href="https://vega.github.io/editor/#/url/vega-lite/N4IgJAzgxgFgpgWwIYgFwhgF0wBwqgegIDc4BzJAOjIEtMYBXAI0poHsDp5kTykBaADZ04JACyUAVhDYA7EABoQAEySYUqUAwBOgtCrVICAM2FksEfgCYA1lJnylxttuSY0oHEm0Q4Hg5h+6KqBIAC+EUqY2kiyEM6uaADaoFBIglAMgmpBGGw6EAAUIQwIlCFwAJSKIEgQ+pg0CH5hALpK2nA4cGr+UGyCpfKoSSo0EOqyUH5KynDZAJ41jc0grWFKEN1Q-jD9U70joL6CcFCNcv5M2gwQMP6YC936NLKB2sTpNXBTbMqvZHqIxAAA81pEQMhtDZ9ExvN9fv9ZGR-GDNCBjDR5sp9C4aLRHCBHs90C4kV8NiAluikGQyJ0KKF0P0GG9lk9cgBHBixRrqRqkcJKfqCFz+T6DXIAYmUsvCkVAizg2mSx3mZwuw1A11u93RxNyr3eEoR-SRgOSoPBlKhMPQcJVSh+ZoBqP8mOx-k63UOIBFQyFICYr38yBBwbiaCsAAZKQb9NzeXQ1DRBZTqaBafS+Ey-fk2VEOQmeW9kwKWsKBmL0RKGNLZTiIm0NqBorF4i4EKqMTRBO9-CcNexhkGbnd5e1Id47UH4U7Ea70WjQB7BDj0d6eu5mQMA5SI6GkOHXkCY3Gi+hE6X+amK1T-FmGTl9CyC0SLyAr3yU2mIuswkAA" rel="nofollow noreferrer">Open the Chart in the Vega Editor</a></p>
  
  <p>Thanks for the help!</p>