Bar Chart showing Initials of Month Names

Using labelExpr to show only initial letters of month names.

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Vega-Lite JSON Specification

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "description": "Using `labelExpr` to show only initial letters of month names.",
  "data": {"url": "data/seattle-weather.csv"},
  "mark": "bar",
  "encoding": {
    "x": {
      "timeUnit": "month",
      "field": "date",
      "axis": {
        "labelAlign": "left",
        "labelExpr": "datum.label[0]"
      }
    },
    "y": {"aggregate": "mean", "field": "precipitation"}
  }
}