Maxkit: VEGA-lite

2022/09/19

VEGA-lite

vega 是一種描述圖表的語法，符合 JSON spec。d3.js 是比較低階的語法，需要用 javascript 處理。vega 只需要 JSON 文件，就撰寫出各式圖表。如果只需要一些常用的圖表，還可以使用 vega-lite，會比 vega 更簡捷。

vega 跟 d3.js 一樣，也是 Washington Interactive Data Lab 開發的，所以 vega 的底層是 d3.js。vega 並不是要取代 d3.js，而是在 d3.js 的基礎上，提供更高階的圖表語言。而且 JSON 更容易用程式碼產生出來。

可以直接從 Example Gallery | Vega-Lite 查看支援的圖表，然後根據自己想要使用的圖表，看範例去修改。

BarChart

Simple bar chart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "A simple bar chart with embedded data.",
  "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}
    ]
  },
  "mark": "bar",
  "encoding": {
    "x": {"field": "a", "type": "nominal", "axis": {"labelAngle": 0}},
    "y": {"field": "b", "type": "quantitative"}
  }
}

render

Arrgegate Bar Chart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "A bar chart showing the US population distribution of age groups in 2000.",
  "height": {"step": 17},
  "data": { "url": "https://vega.github.io/vega-lite/examples/data/population.json"},
  "transform": [{"filter": "datum.year == 2000"}],
  "mark": "bar",
  "encoding": {
    "y": {"field": "age"},
    "x": {
      "aggregate": "sum", "field": "people",
      "title": "population"
    }
  }
}

render

Group Bar Chart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "values": [
      {"category":"A", "group": "x", "value":0.1},
      {"category":"A", "group": "y", "value":0.6},
      {"category":"A", "group": "z", "value":0.9},
      {"category":"B", "group": "x", "value":0.7},
      {"category":"B", "group": "y", "value":0.2},
      {"category":"B", "group": "z", "value":1.1},
      {"category":"C", "group": "x", "value":0.6},
      {"category":"C", "group": "y", "value":0.1},
      {"category":"C", "group": "z", "value":0.2}
    ]
  },
  "mark": "bar",
  "encoding": {
    "x": {"field": "category"},
    "y": {"field": "value", "type": "quantitative"},
    "xOffset": {"field": "group"},
    "color": {"field": "group"}
  }
}

render

Stacked Bar Chart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {"url": "https://vega.github.io/vega-lite/examples/data/seattle-weather.csv"},
  "mark": "bar",
  "encoding": {
    "x": {
      "timeUnit": "month",
      "field": "date",
      "type": "ordinal",
      "title": "Month of the year"
    },
    "y": {
      "aggregate": "count",
      "type": "quantitative"
    },
    "color": {
      "field": "weather",
      "type": "nominal",
      "scale": {
        "domain": ["sun", "fog", "drizzle", "rain", "snow"],
        "range": ["#e7ba52", "#c7c7c7", "#aec7e8", "#1f77b4", "#9467bd"]
      },
      "title": "Weather type"
    }
  }
}

render

Histrogram

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {"url": "https://vega.github.io/vega-lite/examples/data/movies.json"},
  "mark": "bar",
  "encoding": {
    "x": {
      "bin": true,
      "field": "IMDB Rating"
    },
    "y": {"aggregate": "count"}
  }
}

render

ScatterPlot

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "A scatterplot showing horsepower and miles per gallons for various cars.",
  "data": {"url": "https://vega.github.io/vega-lite/examples/data/cars.json"},
  "mark": "point",
  "encoding": {
    "x": {"field": "Horsepower", "type": "quantitative"},
    "y": {"field": "Miles_per_Gallon", "type": "quantitative"}
  }
}

render

LineChart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "Stock prices of 5 Tech Companies over Time.",
  "data": {"url": "https://vega.github.io/vega-lite/examples/data/stocks.csv"},
  "mark": {
    "type": "line",
    "point": true
  },
  "encoding": {
    "x": {"timeUnit": "year", "field": "date"},
    "y": {"aggregate":"mean", "field": "price", "type": "quantitative"},
    "color": {"field": "symbol", "type": "nominal"}
  }
}

render

AreaChart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "width": 300,
  "height": 200,
  "data": {"url": "https://vega.github.io/vega-lite/examples/data/unemployment-across-industries.json"},
  "mark": "area",
  "encoding": {
    "x": {
      "timeUnit": "yearmonth", "field": "date",
      "axis": {"format": "%Y"}
    },
    "y": {
      "aggregate": "sum", "field": "count",
      "title": "count"
    }
  }
}

render

Table-based Plots

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {"url": "https://vega.github.io/vega-lite/examples/data/cars.json"},
  "mark": "rect",
  "encoding": {
    "y": {"field": "Origin", "type": "nominal"},
    "x": {"field": "Cylinders", "type": "ordinal"},
    "color": {"aggregate": "mean", "field": "Horsepower"}
  },
  "config": {
    "axis": {"grid": true, "tickBand": "extent"}
  }
}

render

Circulat Plots

PieChart

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "A simple pie chart with labels.",
  "data": {
    "values": [
      {"category": "a", "value": 4},
      {"category": "b", "value": 6},
      {"category": "c", "value": 10},
      {"category": "d", "value": 3},
      {"category": "e", "value": 7},
      {"category": "f", "value": 8}
    ]
  },
  "encoding": {
    "theta": {"field": "value", "type": "quantitative", "stack": true},
    "color": {"field": "category", "type": "nominal", "legend": null}
  },
  "layer": [{
    "mark": {"type": "arc", "outerRadius": 80}
  }, {
    "mark": {"type": "text", "radius": 90},
    "encoding": {
      "text": {"field": "category", "type": "nominal"}
    }
  }]
}

render