vega-lite - 在 vega lite 中对多面图表的行进行排序

Question

row按每行的项目数对编码中的子图表进行排序有什么魔力吗？

在这个带有汽车数据集的示例中，我希望美国位于顶部，因为它包含最多的项目，然后是日本，然后是欧洲：

也许与items行标题数据存储的属性有关？

标签： vega-lite

Answer 1

我使用聚合转换来计算每个 Origin 和 Cylinder 的项目数，然后使用连接聚合转换来总结每个 Origin 的项目数：

  "transform": [{
      "aggregate": [{"op": "count", "as": "Count"}],
      "groupby": ["Cylinders", "Origin"]
    },
    {
      "joinaggregate": [{"op": "sum", "field": "Count", "as": "OriginCount"}],
      "groupby": ["Origin"]
    }
  ]

然后我可以Count在 x 轴上显示为任何其他数据变量，并row通过计算对编码进行排序OriginCount：

  "encoding": {
    "row": {
      "field": "Origin", "type": "nominal",
      "sort": { "field": "OriginCount", "order": "descending"}
    },
    "x": {
      "field": "Count", "type": "quantitative"
    },
    ...
]

给我以下分组条形图：

请参阅Vega 编辑器 中的完整规范以供参考：

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "data": { "url": "https://vega.github.io/editor/data/cars.json"},
  "transform": [{
      "aggregate": [{"op": "count", "as": "Count"}],
      "groupby": ["Cylinders", "Origin"]
    },
    {
      "joinaggregate": [{"op": "sum", "field": "Count", "as": "OriginCount"}],
      "groupby": ["Origin"]
    }
  ],
  "mark": {
    "type": "bar",
    "tooltip": true
  },
  "width": 400,
  "encoding": {
    "row": {
      "field": "Origin", "type": "nominal",
      "sort": { "field": "OriginCount", "order": "descending"}
    },
    "x": {
      "field": "Count", "type": "quantitative"
    },
    "y": {
      "field": "Cylinders", "type": "nominal"
    }
  }
}