如何使用 Vega-Lite 在轴上绘制多个变量？

按照 Vega-Lite 的西雅图天气教程，很容易绘制出每月的平均最低气温：

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "data": {
    "url": "https://vega.github.io/vega-lite/data/seattle-weather.csv"
  },
  "mark": "line",
  "encoding": {
    "x": {
      "timeUnit": "month",
      "field": "date",
      "type": "temporal"
    },
    "y": {
      "aggregate": "mean",
      "field": "temp_min",
      "type": "quantitative"
    }
  }
}

该数据集还有temp_max多变的。我怎样才能绘制两者temp_min and temp_max在 y 轴上？

您可以按照如下所述使用分层https://vega.github.io/vega-lite/docs/layer.html.

{
  "data": {"url": "data/seattle-weather.csv"},
  "layer": [
    {
      "mark": "line",
      "encoding": {
        "x": {
          "timeUnit": "month",
          "field": "date",
          "type": "temporal"
        },
        "y": {
          "aggregate": "mean",
          "field": "temp_min",
          "type": "quantitative"
        }
      }
    },
    {
      "mark": "line",
      "encoding": {
        "x": {
          "timeUnit": "month",
          "field": "date",
          "type": "temporal"
        },
        "y": {
          "aggregate": "mean",
          "field": "temp_max",
          "type": "quantitative"
        }
      }
    }
  ]
}