Is there a way to pass the aggregated value to the tooltip encoding on a simple histogram in Vega Lite

Question

I would like to add the value of the count to the tooltip in the simple way to a simple histogram plot in Vega Lite?

Something like this:

{
  "data": {
    "url": "data/movies.json"
  },
  "mark": "bar",
  "encoding": {
    "tooltip": [
      {
        "field":  "Count of Records",
        "type": "quantitative"
      }
    ],
    "x": {
      "bin": true,
      "field": "IMDB_Rating",
      "type": "quantitative"
    },
    "y": {
      "aggregate": "count",
      "type": "quantitative"
    }
  }
}

There does not seem to be a way to reference the aggregated y encoding in the tooltip encoding.

Answer 1

Tooltips are encodings just like any other; you can pass the same arguments to the tooltip that you do to the y encoding:

{
  "data": {
    "url": "data/movies.json"
  },
  "mark": "bar",
  "encoding": {
    "tooltip": [
      {
        "aggregate": "count",
        "type": "quantitative"
      }
    ],
    "x": {
      "bin": true,
      "field": "IMDB_Rating",
      "type": "quantitative"
    },
    "y": {
      "aggregate": "count",
      "type": "quantitative"
    }
  }
}

See it in action here.