{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "Using `labelExpr` to show only initial letters of month names.",
  "background": "white",
  "padding": 5,
  "width": 500,
  "height": 200,
  "style": "cell",
  "data": [
    {
      "name": "source_0",
      "url": "https://raw.githubusercontent.com/vega/vega-datasets/master/data/seattle-weather.csv",
      "format": {"type": "csv", "parse": {"date": "date"}, "delimiter": ","},
      "transform": [
        {
          "field": "date",
          "type": "timeunit",
          "units": ["year", "quarter"],
          "as": ["month_date", "month_date_end"]
        },
        {
          "type": "aggregate",
          "groupby": ["month_date", "month_date_end"],
          "ops": ["mean"],
          "fields": ["precipitation"],
          "as": ["mean_precipitation"]
        },
        {
          "type": "filter",
          "expr": "(isDate(datum[\"month_date\"]) || (isValid(datum[\"month_date\"]) && isFinite(+datum[\"month_date\"]))) && isValid(datum[\"mean_precipitation\"]) && isFinite(+datum[\"mean_precipitation\"])"
        }
      ]
    }
  ],
  "marks": [
    {
      "name": "marks",
      "type": "rect",
      "style": ["bar"],
      "from": {"data": "source_0"},
      "encode": {
        "update": {
          "fill": {"value": "#4c78a8"},
          "ariaRoleDescription": {"value": "bar"},
          "description": {
            "signal": "\"date (month): \" + (timeFormat(datum[\"month_date\"], timeUnitSpecifier([\"month\"], {\"year-month\":\"%b %Y \",\"year-month-date\":\"%b %d, %Y \"}))) + \"; Mean of precipitation: \" + (format(datum[\"mean_precipitation\"], \"\"))"
          },
          "x2": [
            {
              "test": "!isValid(datum[\"month_date\"]) || !isFinite(+datum[\"month_date\"])",
              "value": 0
            },
            {"scale": "x", "field": "month_date", "offset": 1}
          ],
          "x": [
            {
              "test": "!isValid(datum[\"month_date\"]) || !isFinite(+datum[\"month_date\"])",
              "value": 0
            },
            {"scale": "x", "field": "month_date_end"}
          ],
          "y": {"scale": "y", "field": "mean_precipitation"},
          "y2": {"scale": "y", "value": 0}
        }
      }
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "time",
      "domain": {
        "data": "source_0",
        "fields": ["month_date", "month_date_end"]
      },
      "range": [0, {"signal": "width"}]
    },
    {
      "name": "y",
      "type": "linear",
      "domain": {"data": "source_0", "field": "mean_precipitation"},
      "range": [{"signal": "height"}, 0],
      "nice": true,
      "zero": true
    }
  ],
  "axes": [
    {
      "scale": "x",
      "orient": "bottom",
      "gridScale": "y",
      "grid": true,
      "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": "y",
      "orient": "left",
      "grid": false,
      "title": "Mean of precipitation",
      "labelOverlap": true,
      "tickCount": {"signal": "ceil(height/40)"},
      "zindex": 0
    }
  ]
}