Vega-Lite文档: 02_data

数据集data

Offical documentation

数据集`data`

与Vega一致, 默认的Vega-Lite中的数据是列表
可以是嵌入的数据值values, 也可以是外链数据url, 还可以是命名数据源name用来绑定上层数据集
Vega-Lite还提供简单的数据生成方法

嵌入数据`values`

P	T	D
values	Array	数据向量
name	String	名字
format	DataFormat	数据格式

嵌入数据的方式:

// 1. 最常规: 指定表头=>值映射关系的二维数组:
"data": {
    "values": [
      {"a": "A", "b": 28}, {"a": "B", "b": 55}, {"a": "C", "b": 43},
      {"a": "D", "b": 91}, {"a": "E", "b": 81}, {"a": "F", "b": 53},
      {"a": "G", "b": 19}, {"a": "H", "b": 87}, {"a": "I", "b": 52}
    ]
},

// 2. 简单的数组会被自动展开, 添加默认表头信息
[5, 3, 8, 1] //会被加载成:
[{"data": 5}, {"data": 3}, {"data": 8}, {"data": 1}]

// 3. 输入字符串和指定的预设格式类型
"data": {
    "values": "a\n1\n2\n3\n4",
    "format": {
        "type": "csv"
    }
},

外链数据`url`

支持url, name, format属性。

默认format是json

命名数据`name`

这个平时很少用到, 暂略。

数据格式`format`

format支持如下属性:

P	T	D
type	String	`json, csv, tsv, dsv`, 默认`json`
parse	Object/Null	指定数据中某一列解析成某种格式: `number, boolean, date`, 如: `"parse":{"col1": "date: '%m%d%Y'"}`

dsv: delimited text file, 分隔符必须是单个字符

数据生成器

`sequence`

根据起止和步长生成系列连续数值, 默认情况下数据的列名为data, 可以用as参数更改列名

Property	Type	Description
start	Number	Required. The starting value of the sequence (inclusive).
stop	Number	Required. The ending value of the sequence (exclusive).
step	Number	The step value between sequence entries.Default value: 1
as	String	The name of the generated sequence field.Default value: "data"

{
    "width": 300,
    "height": 150,
    "data": {"sequence": {
             "start": 0, "stop": 12.7, 
             "step": 0.1, "as": "x"}},
    "transform": [{"calculate": "sin(datum.x)", "as": "sin(x)"}],
    "mark": "line",
    "encoding": {
        "x": {"field": "x", "type": "quantitative"},
        "y": {"field": "sin(x)", "type": "quantitative"}
    }
}

`graticule`

根据经纬度生成地图数据GeoJSON:

Property	Type	Description
extent	Array	Sets both the major and minor extents to the same values.
extentMajor	Array	The major extent of the graticule as a two-element array of coordinates.
extentMinor	Array	The minor extent of the graticule as a two-element array of coordinates.
precision	Number	The precision of the graticule in degrees.Default value: 2.5
step	Array	Sets both the major and minor step angles to the same values.
stepMajor	Array	The major step angles of the graticule.Default value: [90, 360]
stepMinor	Array	The minor step angles of the graticule.Default value: [10, 10]

{
    "width": 400,
    "height": 400,
    "projection": {
        "type": "orthographic",
        "scale": 100,
        "translate": [100,100]
    },
    "layer": [
        {
        "data": {"sphere": true},
        "mark": {
            "type": "geoshape",
            "fill": "aliceblue"
        }
        },
        {
        "data": {"graticule": true},
        "mark": {
            "type": "geoshape",
            "stroke": "black",
            "strokeWidth": 0.5
        }
        }
    ]
}