在 Vega Lite 中使用数据作为数组而不是表

如何在 VegaLite 中使用数组数据？

我想将数据用作数组

dates   = [1, 2, 3]
prices1 = [1, 2, 1]
prices2 = [1.5, 1, 2]

而不是 VegaLite 中传统使用的表数据

[
  { "date": 1, "price": 1, "symbol": 1 },
  { "date": 2, "price": 2, "symbol": 1 },
  { "date": 3, "price": 1, "symbol": 1 },

  { "date": 1, "price": 1.5, "symbol": 2 },
  { "date": 2, "price": 1,   "symbol": 2 },
  { "date": 3, "price": 2,   "symbol": 2 }
]

完整示例操场 https://vega.github.io/editor/#/url/vega-lite/AQ4bwKFUCIBIDOBjAFgUwLYEMYC5gwoAuRADgrgPSUBuaA5lgHT0CWRKArgEZOsD2lZOmy0GWALQAbdmloAWJgCsE-AHYwANFGgEAJmmQAnVqSICN+GAGUi-JAGtgpE0kPB+AM2ABWYABU0VGAAYX4MUiw1Vnd+OiMA1gw0Ji0daBg9LCIcfEhdWBosKU5DPGAAbXSC8H1stHKARk0CF1Y3JpaYBABPDG5+KSbgAF9tGtAwOqIG-AAmLraO+a7e-sHhseqCqcz68oBmRddZ4GaCNYGh-EbR7W3dXayZztaTpqYfVb6r8rm7h7QJ77FZvdqnc4gbo-DbzAETEDAl74I5g5bABawS6wjGjQHAAC6Dy2BRg2CMDnK+RqMCIPVIpxgMjUDXGNNI-FYaiIVPxUM8rCkUjQenKnmKCDQbImMAFQvKMAA7ihZDB8SNidLYGg1Eh+HoufReTKAB5U2UxKSiqzPVkEOkMhUAR04UXMOXMdBgJJpPXNArQVoVSzttPpjJdbvY2VYXp9pL1Un4Rn9lutFxhQy6DsZanCXOK3uJ1Q1ECAA

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "description": "Stock prices of 5 Tech Companies over Time.",
  "data": {
    "values": [
      { "date": 1, "price": 1, "symbol": 1 },
      { "date": 2, "price": 2, "symbol": 1 },
      { "date": 3, "price": 1, "symbol": 1 },

      { "date": 1, "price": 1.5, "symbol": 2 },
      { "date": 2, "price": 1,   "symbol": 2 },
      { "date": 3, "price": 2,   "symbol": 2 }
    ]
  },
  "mark": {
    "type": "line",
    "point": {
      "filled": false,
      "fill": "white"
    }
  },
  "encoding": {
    "x": {"field": "date", "type": "quantitative"},
    "y": {"field": "price", "type": "quantitative"},
    "color": {"field": "symbol", "type": "nominal"}
  }
}

您可以使用一系列数据转换来实现此目的：

1. A 展平变换 https://vega.github.io/vega-lite/docs/flatten.html将数据数组转换为普通表条目
2. A 折叠变换 https://vega.github.io/vega-lite/docs/fold.html将两个价格列转换为带有一列标签的单个价格列
3. A 计算变换 https://vega.github.io/vega-lite/docs/calculate.html使用适当的织女星表达 https://vega.github.io/vega/docs/expressions/从价格标签中提取号码。

结果是这样的：

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "description": "Stock prices of 5 Tech Companies over Time.",
  "data": {
    "values": [
      {"date": [1, 2, 3], "prices1": [1, 2, 1], "prices2": [1.5, 1, 2]}
    ]
  },
  "transform": [
    {"flatten": ["date", "prices1", "prices2"]},
    {"fold": ["prices1", "prices2"], "as": ["symbol", "price"]},
    {"calculate": "slice(datum.symbol, -1)", "as": "symbol"}
  ],
  "mark": {"type": "line", "point": {"filled": false, "fill": "white"}},
  "encoding": {
    "x": {"field": "date", "type": "quantitative"},
    "y": {"field": "price", "type": "quantitative"},
    "color": {"field": "symbol", "type": "nominal"}
  }
}

要探索转换正在执行的操作，在以下位置打开图表可能会很有用：维加编辑器 https://vega.github.io/editor/#/url/vega-lite/N4KABGBEAkDODGALApgWwIaQFxUQFzwAdYsB6UgN2QHN0A6agSz0QFcAjOxge1IRQyUa6ALQAbZskoAWOgCtY3AHaQANOCgATZAgBOjQnh4qckAMp5u8ANZhC++DrDcAZmACsYACrIkYAMLcqIToSoxO3FS63oyoyHRqGpCa6HiYOKAQEJAU6GKsOthgANoaWWDAyanIRcUAjKpgAEyNAMwAuo2Q9oyOsHW1Dc2NdZ1QPX1Ng3TuI41N7QC+ZWDtGovq2Xi6obAu3LqotSuVLmKpeMgmJVWXauMOOgNdEzpTS5tZp9ximrXdj369wBvTekDGkHQsH+sAAnqh2D9ga9wRsTpB4Hl4KxzndTLAJI4ABQpPCsVB0OEIn6NER1ACUwKhRUgVMRYkgywgnSSGF01iKlTwsMINVMEiUNRe3EYSjwgsgLkYYjEyD+OBceVgyC6SpVLIA7ohJJy0dkrvBuJpZdRBStIAAPBVK5C-FmkqVQYWilkAR1YoSMaSMVE5n2ysOd4TdphRXW9Yqg-sDzFSjFDZqyGJ+ByjrvVUDZSPjIsTkCUQVleU56xAiyAA并使用数据查看器选项卡来探索每个转换如何修改基础数据。