Vega-lite 限制序号类型的刻度数

Question

我使用了 Vega-lite 条形图的示例，其中我在 x 轴上有一个主要流派，而 y 轴显示了计数。

以下是 vega-lite 配置：

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "description": "A dashboard with cross-highlighting.",
  "data": {"url": "data/movies.json"},
  "width": 330,
  "height": 120,
  "mark": "bar",
  "selection": {"pts": {"type": "single", "encodings": ["x"]}},
  "encoding": {
    "x": {
      "field": "Major Genre",
      "type": "ordinal",
      "axis": {"labelAngle": 0, "labelOverlap": "parity"}
    },
    "y": {"aggregate": "count"},
    "color": {
      "condition": {"selection": "pts", "value": "steelblue"},
      "value": "grey"
    }
  }
}

在此，我在 x 轴中使用了 labelOverlap 配置以避免标签重叠，因此现在标签名称的数量有限。我想减少应该等于标签的 x 轴刻度数。我尝试使用 tickCount 配置，但它似乎适用于定量和时间类型的字段。此外，当我们使用时间时，日期字段显示有限编号。标签和刻度线。所以这种行为是我想用名义和序数类型实现的。

Answer 1

我知道减少名义或有序轴上刻度数的唯一方法是设置 "ticks": false 隐藏 all 个刻度，或者使用 "values" 条目显式设置可见刻度。下面是后者的例子（open in editor）：

{
  "data": {"url": "data/movies.json"},
  "width": 330,
  "height": 120,
  "mark": "bar",
  "selection": {"pts": {"type": "single", "encodings": ["x"]}},
  "encoding": {
    "x": {
      "field": "Major Genre",
      "type": "ordinal",
      "axis": {
        "labelAngle": 0,
        "labelOverlap": "parity",
        "values": [null, "Comedy", "Horror", "Western"]
      }
    },
    "y": {"aggregate": "count"},
    "color": {
      "condition": {"selection": "pts", "value": "steelblue"},
      "value": "grey"
    }
  }
}

Answer 2

我不得不用 x-axis 创建另一个图层，其中隐藏了标签名称并添加了另一个数据对象，其中将包含一些虚拟记录。这不是一种正确的方法，但它似乎可以满足我的用例。因此，无论主要数据标签如何，额外的层都会完成显示刻度的工作。下面是修改后的 vega-lite 配置：

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "description": "A dashboard with cross-highlighting.",
  "data": {"url": "data/movies.json"},
  "width": 320,
  "height": 120,
  "layer": [
    {
      "mark": "bar",
      "selection": {"pts": {"type": "single", "encodings": ["x"]}},
      "encoding": {
        "x": {
          "field": "Major Genre",
          "type": "ordinal",
          "axis": {
            "labelAngle": 0,
            "labelOverlap": "parity",
            "ticks": false,
            "labelPadding": 10
          }
        },
        "y": {"aggregate": "count"},
        "color": {
          "condition": {"selection": "pts", "value": "steelblue"},
          "value": "grey"
        }
      }
    },
    {
      "mark": "text",
      "data": {
        "values": [
          {"Major Genre": "a"},
          {"Major Genre": "b"},
          {"Major Genre": "c"},
          {"Major Genre": "d"}
        ]
      },
      "encoding": {
        "x": {
          "field": "Major Genre",
          "type": "ordinal",
          "axis": {"labels": false, "orient": "bottom", "title": null}
        }
      }
    }
  ],
  "resolve": {"axis": {"x": "independent"}, "scale": {"x": "independent"}}
}

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