Vega view for a visualisation of uk.gov petition data

uk-gov-petitions.json

{
  "width": 800,
  "height": 200,
  "data": [
    {
      "name": "stocks",
      "url": "https://gist.githubusercontent.com/brew/a071efd8fb3dcd28854630d5b8d9ea95/raw/a9d9f9bdfa3c26f960967f0d7897f358106cf3c2/uk-gov-petitions.csv",
      "format": {
        "type": "csv",
        "parse": {"starting": "date:'%Y-%m-%d %H:%M:%S'"}
      },
      "transform": [
        {
          "type": "filter",
          "test": "datum[\"department\"] == \"Ministry of Defence\""
        },
        {
          "type": "formula",
          "field": "starting_day",
          "expr": "datetime(year(datum[\"starting\"]), month(datum[\"starting\"]), 2, 0, 0, 0, 0)"
        },
        {
          "type": "aggregate",
          "groupby": ["starting_day","department"],
          "summarize": [
            {
              "field": "*",
              "ops": ["count"],
              "as": ["dept_count"]
            }
          ]
        }
      ]
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "time",
      "range": "width",
      "domain": {"data": "stocks","field": "starting_day"},
      "nice": "month"
    },
    {
      "name": "x2",
      "type": "ordinal",
      "range": "width",
      "domain": {"data": "stocks","field": "starting_day"}
    },    
    {
      "name": "y",
      "type": "linear",
      "range": "height",
      "nice": true,
      "domain": {"data": "stocks","field": "dept_count"}
    },
    {
      "name": "color",
      "type": "ordinal",
      "domain": {"data": "stocks","field": "department"},
      "range": "category10"
    }
  ],
  "axes": [{"type": "x","scale": "x"},{"type": "y","scale": "y"}],
  "marks": [
    {
      "type": "group",
      "from": {
        "data": "stocks",
        "transform": [{"type": "facet","groupby": ["department"]}]
      },
      "marks": [
        {
          "type": "rect",
          "properties": {
            "enter": {
              "x": {"scale": "x","field": "starting_day"},
              "y": {"scale": "y","field": "dept_count"},
              "y2": {"scale": "y","value": 0},
              "fill": {"scale": "color","field": "department"},
              "width": {"band": true, "scale": "x2", "offset": -1}
            }
          }
        }
      ]
    }
  ]
}