{
  "spec": {
    "data": {"url": "data/cars.json"},
    "mark": "?",
    "encodings": [
      {
        "channel": "?",
        "bin": "?",
        "timeUnit": "?",
        "field": "?",
        "type": "?"
      },
      {
        "channel": "?",
        "field": "*",
        "aggregate": "count",
        "type": "quantitative"
      }
    ]
  },
  "groupBy": ["field", "aggregate", "bin", "timeUnit", "stack"],
  "chooseBy": "effectiveness"
}