gistfile1.txt

{
  "width": 200,
  "height": 200,
  "padding": "auto",
  "data": [
    {
      "name": "source",
      "url": "data/cars.json",
      "format": {"type": "json","parse": {"Acceleration": "number"}},
      "transform": [
        {
          "type": "filter",
          "test": "datum.Acceleration!==null"
        }
      ]
    },
    {
      "name": "summary",
      "source": "source",
      "transform": [
        {
          "type": "aggregate",
          "groupby": ["Cylinders"],
          "summarize": {"Acceleration": ["mean"]}
        }
      ]
    },
    {
      "name": "layout",
      "source": "summary",
      "transform": [
        {
          "type": "aggregate",
          "summarize": [{"field": "Cylinders","ops": ["distinct"]}]
        },
        {
          "type": "formula",
          "field": "cellWidth",
          "expr": "(datum.distinct_Cylinders + 1) * 21"
        }
      ]
    }
  ],
  "marks": [
    {
      "name": "root",
      "type": "group",
      "from": {"data": "layout"},
      "properties": {
        "update": {
          "width": {"field": "cellWidth"},
          "height": {"value": 200}
        }
      },
      "marks": [
        {
          "type": "rect",
          "properties": {
            "update": {
              "xc": {"scale": "x","field": "Cylinders"},
              "width": {"value": 21,"offset": -1},
              "y": {"scale": "y","field": "mean_Acceleration"},
              "y2": {"field": {"group": "height"}},
              "fill": {"value": "#4682b4"}
            }
          },
          "from": {"data": "summary"}
        }
      ],
      "scales": [
        {
          "name": "x",
          "type": "ordinal",
          "domain": {
            "data": "summary",
            "field": "Cylinders",
            "sort": true
          },
          "rangeMin": 0,
          "rangeMax": {"data": "layout","field": "cellWidth"},
          "round": true,
          "clamp": true,
          "bandWidth": 21,
          "padding": 1,
          "points": true
        },
        {
          "name": "y",
          "type": "linear",
          "domain": {
            "data": "summary",
            "field": "mean_Acceleration",
            "sort": true
          },
          "rangeMin": 200,
          "rangeMax": 0,
          "round": true,
          "clamp": true,
          "nice": true
        }
      ],
      "axes": [
        {
          "type": "x",
          "scale": "x",
          "grid": false,
          "ticks": 5,
          "title": "Cylinders",
          "properties": {
            "labels": {
              "angle": {"value": 270},
              "align": {"value": "right"},
              "baseline": {"value": "middle"},
              "text": {"template": "{{ datum.data | truncate:25}}"}
            }
          }
        },
        {
          "type": "y",
          "scale": "y",
          "format": "s",
          "grid": true,
          "layer": "back",
          "title": "MEAN(Acceleration)"
        }
      ]
    }
  ]
}