Multi Series Line Chart with Halo Stroke

Multi-series Line Chart with Halo. Use pivot and repeat-layer as a workaround to facet groups of lines and their halo strokes. See https://github.com/vega/vega-lite/issues/6192 for more discussion.

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Vega-Lite JSON Specification

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "description": "Multi-series Line Chart with Halo. Use pivot and repeat-layer as a workaround to facet groups of lines and their halo strokes. See https://github.com/vega/vega-lite/issues/6192 for more discussion.",
  "data": {"url": "data/stocks.csv"},
  "transform": [{
    "pivot": "symbol",
    "value": "price",
    "groupby": ["date"]
  }],
  "repeat": {
    "layer": ["AAPL", "AMZN", "GOOG", "IBM", "MSFT"]
  },
  "spec": {
    "layer": [{
      "mark": {"type": "line", "stroke": "white", "strokeWidth": 4},
      "encoding": {
        "x": {"field": "date", "type": "temporal"},
        "y": {"field": {"repeat": "layer"}, "type": "quantitative", "title": "price"}
      }
    },{
      "mark": {"type": "line"},
      "encoding": {
        "x": {"field": "date", "type": "temporal"},
        "y": {"field": {"repeat": "layer"}, "type": "quantitative", "title": "price"},
        "stroke": {"datum": {"repeat": "layer"}, "type": "nominal"}
      }
    }]
  }
}