如何为分层线图创建图例

Question

基本上我所拥有的是一个由多个折线图分层而成的折线图。由于每张图只有一条线，没有自动生成图例，那么获取图表图例的最佳方法是什么？我一直在考虑尝试转换我的数据集。这是疾病预防控制中心从 2019 年到 2020 年 6 月的每周死亡总数。csv 的排列方式是每个州的每个日期都有一个记录，其中每种疾病类型作为它自己的列，整数作为列值。所以没有一个领域可以绘制图表，有很多领域，因此是分层的。任何有关如何解决此问题的见解将不胜感激！这是我目前的工作：

https://observablehq.com/@justin-krohn/covid-excess-deaths

Answer 1

您可以通过将每一层的颜色编码设置为 datum 指定您希望它具有的标签来为分层图表创建图例。例如 (vega editor):

{
  "data": {
    "values": [
      {"x": 1, "y1": 1, "y2": 2},
      {"x": 2, "y1": 3, "y2": 1},
      {"x": 3, "y1": 2, "y2": 4},
      {"x": 4, "y1": 4, "y2": 3},
      {"x": 5, "y1": 3, "y2": 5}
    ]
  },
  "encoding": {"x": {"field": "x", "type": "quantitative"}},
  "layer": [
    {
      "mark": "line",
      "encoding": {
        "y": {"field": "y1", "type": "quantitative"},
        "color": {"datum": "y1"}
      }
    },
    {
      "mark": "line",
      "encoding": {
        "y": {"field": "y2", "type": "quantitative"},
        "color": {"datum": "y2"}
      }
    }
  ]
}

或者，您可以使用 Fold Transform to pivot your data so that instead of manual layers, you can plot the multiple lines with a simple color encoding. For example (vega editor):

{
  "data": {
    "values": [
      {"x": 1, "y1": 1, "y2": 2},
      {"x": 2, "y1": 3, "y2": 1},
      {"x": 3, "y1": 2, "y2": 4},
      {"x": 4, "y1": 4, "y2": 3},
      {"x": 5, "y1": 3, "y2": 5}
    ]
  },
  "transform": [{"fold": ["y1", "y2"], "as": ["name", "y"]}],
  "mark": "line",
  "encoding": {
    "x": {"field": "x", "type": "quantitative"},
    "y": {"field": "y", "type": "quantitative"},
    "color": {"field": "name", "type": "nominal"}
  }
}

如何为分层线图创建图例

How do I create a legend for a layered line plot

vega-lite

vega

observablehq