{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "A line graph showing how the overall average Miles Per Gallon for how the MPG has changed over the years. The red line shows the average, and is layered on top of all the raw data.",
  "background": "white",
  "padding": 5,
  "width": 200,
  "height": 200,
  "style": "cell",
  "data": [
    {
      "name": "source_0",
      "url": "data/cars.json",
      "format": {"type": "json", "parse": {"Year": "date"}},
      "transform": [
        {"type": "filter", "expr": "datum.Miles_per_Gallon !== null"},
        {
          "field": "Year",
          "type": "timeunit",
          "units": ["year"],
          "as": ["year", "year_end"]
        },
        {
          "type": "window",
          "params": [null],
          "as": ["Average_MPG"],
          "ops": ["mean"],
          "fields": ["Miles_per_Gallon"],
          "sort": {"field": ["year"], "order": ["ascending"]},
          "ignorePeers": false,
          "frame": [null, 0]
        },
        {
          "field": "Year",
          "type": "timeunit",
          "units": ["year"],
          "as": ["year_Year", "year_Year_end"]
        }
      ]
    },
    {
      "name": "data_0",
      "source": "source_0",
      "transform": [
        {
          "type": "filter",
          "expr": "(isDate(datum[\"year_Year\"]) || (isValid(datum[\"year_Year\"]) && isFinite(+datum[\"year_Year\"]))) && isValid(datum[\"Miles_per_Gallon\"]) && isFinite(+datum[\"Miles_per_Gallon\"])"
        }
      ]
    }
  ],
  "marks": [
    {
      "name": "layer_0_marks",
      "type": "symbol",
      "style": ["circle"],
      "from": {"data": "data_0"},
      "encode": {
        "update": {
          "opacity": {"value": 0.7},
          "fill": {"value": "#4c78a8"},
          "ariaRoleDescription": {"value": "circle"},
          "description": {
            "signal": "\"Year (year): \" + (timeFormat(datum[\"year_Year\"], timeUnitSpecifier([\"year\"], {\"year-month\":\"%b %Y \",\"year-month-date\":\"%b %d, %Y \"}))) + \"; Miles_per_Gallon: \" + (format(datum[\"Miles_per_Gallon\"], \"\"))"
          },
          "x": {"scale": "x", "field": "year_Year"},
          "y": {"scale": "y", "field": "Miles_per_Gallon"},
          "shape": {"value": "circle"}
        }
      }
    },
    {
      "name": "layer_1_marks",
      "type": "line",
      "style": ["line"],
      "sort": {"field": "datum[\"year_Year\"]"},
      "from": {"data": "source_0"},
      "encode": {
        "update": {
          "stroke": {"value": "red"},
          "description": {
            "signal": "\"Year (year): \" + (timeFormat(datum[\"year_Year\"], timeUnitSpecifier([\"year\"], {\"year-month\":\"%b %Y \",\"year-month-date\":\"%b %d, %Y \"}))) + \"; Miles Per Gallon: \" + (format(datum[\"Average_MPG\"], \"\"))"
          },
          "x": {"scale": "x", "field": "year_Year"},
          "y": {"scale": "y", "field": "Average_MPG"},
          "defined": {
            "signal": "isValid(datum[\"year_Year\"]) && isFinite(+datum[\"year_Year\"]) && isValid(datum[\"Average_MPG\"]) && isFinite(+datum[\"Average_MPG\"])"
          }
        }
      }
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "time",
      "domain": {
        "fields": [
          {"data": "data_0", "field": "year_Year"},
          {"data": "source_0", "field": "year_Year"}
        ]
      },
      "range": [0, {"signal": "width"}]
    },
    {
      "name": "y",
      "type": "linear",
      "domain": {
        "fields": [
          {"data": "data_0", "field": "Miles_per_Gallon"},
          {"data": "source_0", "field": "Average_MPG"}
        ]
      },
      "range": [{"signal": "height"}, 0],
      "nice": true,
      "zero": true
    }
  ],
  "axes": [
    {
      "scale": "x",
      "orient": "bottom",
      "gridScale": "y",
      "grid": true,
      "tickCount": {"signal": "ceil(width/40)"},
      "domain": false,
      "labels": false,
      "aria": false,
      "maxExtent": 0,
      "minExtent": 0,
      "ticks": false,
      "zindex": 0
    },
    {
      "scale": "y",
      "orient": "left",
      "gridScale": "x",
      "grid": true,
      "tickCount": {"signal": "ceil(height/40)"},
      "domain": false,
      "labels": false,
      "aria": false,
      "maxExtent": 0,
      "minExtent": 0,
      "ticks": false,
      "zindex": 0
    },
    {
      "scale": "x",
      "orient": "bottom",
      "grid": false,
      "title": "Year (year)",
      "format": {
        "signal": "timeUnitSpecifier([\"year\"], {\"year-month\":\"%b %Y \",\"year-month-date\":\"%b %d, %Y \"})"
      },
      "labelFlush": true,
      "labelOverlap": true,
      "tickCount": {"signal": "ceil(width/40)"},
      "zindex": 0
    },
    {
      "scale": "y",
      "orient": "left",
      "grid": false,
      "title": "Miles Per Gallon",
      "labelOverlap": true,
      "tickCount": {"signal": "ceil(height/40)"},
      "zindex": 0
    }
  ]
}