Vega-Lite中的数据布局，图层和图例

debugcn 发表于 Dev

哈利鲁坦

我的情况很简单，我认为我的解决方案太复杂了，很可能会丢失一些东西。假设我有time，位置（x，y，z），角度（滚动，俯仰，偏航）和速度的度量。我想要一个像现在一样简单的可视化效果，其中速度图可以用作“画笔”以动态放大前两个图。

我在vega编辑器中的情节的一个小例子可以在这里找到。

1.我可以使用其他数据布局吗？

现在，每个点都是一个对象

{
    "pitch": -0.006149084584096612,
    "roll": 0.0007914191778949736,
    "speed": 4.747345444390669,
    "time": 0.519741,
    "x": -0.01731604791076788,
    "y": 0.020068310429957575,
    "yaw": 0.0038123065311157552,
    "z": -0.016005977140476142
}

在许多数据点的情况下，仅用于重复列名就需要大量内存。更好的是将数据具有以下形式

{
    "time": [t1, t2, t3, ...],
    "x": [...],
    ...
}

but vega's "row first" representation doesn't allow for that. I already asked on Slack where someone suggested to use Fold and Pivot, but I'm not sure how to implement this. Is it possible to use data that are stored as arrays? I'm creating the data myself from a C++ program and I'm free to export a different representation easily. The only question is how do I make vega-lite understand?

2. Layers and legends.

If I had time-series data with an "indicator column", I could create plots that combine several graphs easily. Unfortunately, I don't have that and the only solution I found is to use layers. With this, I have to set the colours for different graphs explicitly (instead of using schemes) and I don't get a legend.

如果层实际上是唯一的选择，例如将x，y，z合并成一个“运动”图，那么如何获得该图例的图例，告诉我红色-> x，绿色-> y和蓝色-> z？

jakevdp

答案是肯定的。

第一个问题的关键是以密集格式传递数据并使用Flatten变换对其进行扩展。

第二个问题的关键是使用折叠转换将多列转换为一个指标加一个值。

这是单个图表（在编辑器中打开）的演示：

{
  "data": {
    "values": [
      {
        "time": [1, 2, 3, 4],
        "x": [5, 4, 5, 2],
        "y": [2, 3, 2, 4],
        "z": [1, 2, 1, 0]
      }
    ]
  },
  "transform": [
    {"flatten": ["time", "x", "y", "z"]},
    {"fold": ["x", "y", "z"], "as": ["column", "value"]}
  ],
  "mark": "line",
  "encoding": {
    "x": {"field": "time", "type": "quantitative"},
    "y": {"field": "value", "type": "quantitative"},
    "color": {"field": "column", "type": "nominal"}
  }
}

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编辑于2021-04-5

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