如何在 Altair 中使用 Vega/Vega-Lite 规格，例如创建圆形包装图？

Vega 本身通过以下方式提供循环包装包变换 https://vega.github.io/vega/docs/transforms/pack/。你可以找到一个示例图here https://vega.github.io/vega/examples/circle-packing/.

我在中找不到包转换Altair 文档 https://altair-viz.github.io/user_guide/transform/index.html。它是否以某种方式暴露或者我可以轻松添加它？我想，我总是可以修改 JSON Vega 规范，但这可能有点脆弱。

Altair 构建在 Vega-Lite 之上，而不是直接构建在 Vega 之上。因此，Altair 中可用的变换是Vega-Lite 中指定的那些 https://vega.github.io/vega-lite/docs/transform.html。话虽如此，您可以直接在 Altair 中运行 Vega 规范，如下所示：

from altair.vega import Vega

Vega({
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "An example of a circle packing layout for hierarchical data.",
  "width": 600,
  "height": 600,
  "padding": 5,
  "autosize": "none",

  "data": [
    {
      "name": "tree",
      "url": "https://raw.githubusercontent.com/vega/vega/main/docs/data/flare.json",
      "transform": [
        {
          "type": "stratify",
          "key": "id",
          "parentKey": "parent"
        },
        {
          "type": "pack",
          "field": "size",
          "sort": {"field": "value"},
          "size": [{"signal": "width"}, {"signal": "height"}]
        }
      ]
    }
  ],

  "scales": [
    {
      "name": "color",
      "type": "ordinal",
      "domain": {"data": "tree", "field": "depth"},
      "range": {"scheme": "category20"}
    }
  ],

  "marks": [
    {
      "type": "symbol",
      "from": {"data": "tree"},
      "encode": {
        "enter": {
          "shape": {"value": "circle"},
          "fill": {"scale": "color", "field": "depth"},
          "tooltip": {"signal": "datum.name + (datum.size ? ', ' + datum.size + ' bytes' : '')"}
        },
        "update": {
          "x": {"field": "x"},
          "y": {"field": "y"},
          "size": {"signal": "4 * datum.r * datum.r"},
          "stroke": {"value": "white"},
          "strokeWidth": {"value": 0.5}
        },
        "hover": {
          "stroke": {"value": "red"},
          "strokeWidth": {"value": 2}
        }
      }
    }
  ]
})

请注意 Altair 中的 Vega 包装器可能会在未来版本中被弃用 https://github.com/altair-viz/altair/issues/2817因为现在可以使用 IPython 显示 Vega 和 Vega-Lite 规格：

import json
from IPython.display import display

vg_spec = r"""{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "description": "An example of a circle packing layout for hierarchical data.",
  "width": 600,
  "height": 600,
  "padding": 5,
  "autosize": "none",

  "data": [
    {
      "name": "tree",
      "url": "https://raw.githubusercontent.com/vega/vega/main/docs/data/flare.json",
      "transform": [
        {
          "type": "stratify",
          "key": "id",
          "parentKey": "parent"
        },
        {
          "type": "pack",
          "field": "size",
          "sort": {"field": "value"},
          "size": [{"signal": "width"}, {"signal": "height"}]
        }
      ]
    }
  ],

  "scales": [
    {
      "name": "color",
      "type": "ordinal",
      "domain": {"data": "tree", "field": "depth"},
      "range": {"scheme": "category20"}
    }
  ],

  "marks": [
    {
      "type": "symbol",
      "from": {"data": "tree"},
      "encode": {
        "enter": {
          "shape": {"value": "circle"},
          "fill": {"scale": "color", "field": "depth"},
          "tooltip": {"signal": "datum.name + (datum.size ? ', ' + datum.size + ' bytes' : '')"}
        },
        "update": {
          "x": {"field": "x"},
          "y": {"field": "y"},
          "size": {"signal": "4 * datum.r * datum.r"},
          "stroke": {"value": "white"},
          "strokeWidth": {"value": 0.5}
        },
        "hover": {
          "stroke": {"value": "red"},
          "strokeWidth": {"value": 2}
        }
      }
    }
  ]
}
"""

display({"application/vnd.vega.v5+json": json.loads(vg_spec)}, raw=True)