Vega Lite 中分组条形图的嵌套轴标签

Question

我正在使用 Vega-Lite 构建分组条形图。每个数据点都有一个count、一个sample 和一个fdr 值。这些条按sample 分组，在这些组中，我希望每个fdr-value 一个条。我能够使用以下规范完成所有这些工作（click here 用于 Vega 编辑器中的版本）：

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "values": [
      {"count": 87, "organism": "Thaliana", "sample": "S01", "fdr": "0.1%"},
      {"count": 231, "organism": "Spider", "sample": "S01", "fdr": "0.1%"},
      {"count": 40, "organism": "Thaliana", "sample": "S01", "fdr": "1%"},
      {"count": 560, "organism": "Spider", "sample": "S01", "fdr": "1%"},
      {"count": 11.33, "organism": "Thaliana", "sample": "S02", "fdr": "0.1%"},
      {"count": 88.67, "organism": "Spider", "sample": "S02", "fdr": "0.1%"},
      {"count": 70, "organism": "Thaliana", "sample": "S02", "fdr": "1%"},
      {"count": 30, "organism": "Spider", "sample": "S02", "fdr": "1%"}
    ]
  },
  "width": "container",
  "layer": [
    {
      "mark": "bar",
      "encoding": {
        "x": {
          "aggregate": "sum",
          "field": "count",
          "stack": "normalize",
          "title": "Distribution (%)",
          "sort": "descending",
          "axis": {"labelFontSize": 14, "titleFontSize": 20}
        },
        "y": {
          "field": "sample",
          "title": "Sample name",
          "axis": {
            "labelFontSize": 14,
            "titleFontSize": 20,
            "labelLimit": 500,
            "labelExpr": "datum.label"
          }
        },
        "yOffset": {"field": "fdr", "scale": {"paddingInner": 0.1}},
        "color": {"field": "organism", "legend": {"title": "Species"}}
      }
    }
  ],
  "config": {
    "legend": {
      "orient": "bottom",
      "direction": "vertical",
      "columns": 4,
      "labelFontSize": 14,
      "titleFontSize": 16,
      "labelLimit": 250,
      "symbolSize": 150
    }
  }
}

当前可视化的屏幕截图：

现在，我遇到的问题是我还想添加一个标签，显示每个柱的fdr-值（因为每个柱只对应一个fdr）。但我无法让它工作，因为yOffset 通道不支持它自己的轴。

关于我如何做到这一点的任何想法？

编辑：这是我想要实现的大致目标的示例：

Answer 1

你的意思是这样吗？

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "values": [
      {"count": 87, "organism": "Thaliana", "sample": "S01", "fdr": "0.1%"},
      {"count": 231, "organism": "Spider", "sample": "S01", "fdr": "0.1%"},
      {"count": 40, "organism": "Thaliana", "sample": "S01", "fdr": "1%"},
      {"count": 560, "organism": "Spider", "sample": "S01", "fdr": "1%"},
      {"count": 11.33, "organism": "Thaliana", "sample": "S02", "fdr": "0.1%"},
      {"count": 88.67, "organism": "Spider", "sample": "S02", "fdr": "0.1%"},
      {"count": 70, "organism": "Thaliana", "sample": "S02", "fdr": "1%"},
      {"count": 30, "organism": "Spider", "sample": "S02", "fdr": "1%"}
    ]
  },
  "width": "container",
  "encoding": {
    "y": {
      "field": "sample",
      "title": "Sample name",
      "axis": {
        "labelFontSize": 14,
        "titleFontSize": 20,
        "labelLimit": 500,
        "labelExpr": "datum.label"
      }
    },
    "yOffset": {"field": "fdr", "scale": {"paddingInner": 0.1}}
  },
  "layer": [
    {
      "mark": "bar",
      "encoding": {
        "x": {
          "aggregate": "sum",
          "field": "count",
          "stack": "normalize",
          "title": "Distribution (%)",
          "sort": "descending",
          "axis": {"labelFontSize": 14, "titleFontSize": 20}
        },
        "color": {"field": "organism", "legend": {"title": "Species"}}
      }
    },
    {
      "mark": {"type": "text", "opacity": 0.9},
      "encoding": {
        "x": {
          "aggregate": "sum",
          "field": "count",
          "sort": "descending",
          "stack": "normalize",
          "bandPosition": 0.5
        },
        "text": {"field": "fdr"},
        "detail": {"field": "organism"},
        "color": {"value": "white"}
      }
    }
  ],
  "config": {
    "legend": {
      "orient": "bottom",
      "direction": "vertical",
      "columns": 4,
      "labelFontSize": 14,
      "titleFontSize": 16,
      "labelLimit": 250,
      "symbolSize": 150
    }
  }
}