Multi Series Line Chart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "description": "Stock prices of 5 Tech Companies over Time.",
  "data": {"url": "data/stocks.csv"},
  "mark": "line",
  "encoding": {
    "x": {"field": "date", "type": "temporal", "axis": {"format": "%Y"}},
    "y": {"field": "price", "type": "quantitative"},
    "color": {"field": "symbol", "type": "nominal"}
  }
}