vega-lite

What is vega-lite?

Vega-Lite is a high-level grammar of interactive graphics. It provides a concise JSON syntax for rapidly generating visualizations to support analysis. Vega-Lite specifications can be compiled to Vega specifications.

What are vega-lite's main functionalities?

Basic Chart

This code sample demonstrates how to create a simple bar chart using Vega-Lite. The data is embedded directly in the specification, and the chart maps the 'a' field to the x-axis and the 'b' field to the y-axis.

{
  "$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"}
  }
}

Interactive Chart

This code sample demonstrates how to create an interactive scatterplot using Vega-Lite. The chart allows users to select a region (brush) to highlight points based on the 'Cylinders' field.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "A scatterplot with interactive selection.",
  "data": {"url": "data/cars.json"},
  "mark": "point",
  "encoding": {
    "x": {"field": "Horsepower", "type": "quantitative"},
    "y": {"field": "Miles_per_Gallon", "type": "quantitative"},
    "color": {
      "condition": {
        "selection": "brush",
        "field": "Cylinders",
        "type": "ordinal"
      },
      "value": "grey"
    }
  },
  "selection": {
    "brush": {"type": "interval"}
  }
}

Layered Chart

This code sample demonstrates how to create a layered chart using Vega-Lite. The chart combines a line mark and a point mark to visualize stock prices over time.

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "description": "A layered chart with a line and point marks.",
  "data": {"url": "data/stocks.csv"},
  "layer": [
    {
      "mark": "line",
      "encoding": {
        "x": {"field": "date", "type": "temporal"},
        "y": {"field": "price", "type": "quantitative"},
        "color": {"field": "symbol", "type": "nominal"}
      }
    },
    {
      "mark": "point",
      "encoding": {
        "x": {"field": "date", "type": "temporal"},
        "y": {"field": "price", "type": "quantitative"},
        "color": {"field": "symbol", "type": "nominal"}
      }
    }
  ]
}

Other packages similar to vega-lite

plotly.js

Plotly.js is a high-level, declarative charting library. It supports a wide range of chart types and is highly interactive. Compared to Vega-Lite, Plotly.js offers more built-in interactivity and a broader range of chart types, but it can be more complex to use.

chart.js

Chart.js is a simple yet flexible JavaScript charting library. It offers a variety of chart types and is easy to use for basic visualizations. Compared to Vega-Lite, Chart.js is more straightforward but less powerful for complex, interactive visualizations.

d3

D3.js is a powerful JavaScript library for creating data-driven documents. It provides fine-grained control over the visual appearance and behavior of charts. Compared to Vega-Lite, D3.js offers more flexibility and customization options but requires more effort and expertise to use effectively.

README

Vega-lite

Vega-lite is work in progress and we are working on improving the code and documentation.

Provides a higher-level grammar for visual analysis, comparable to ggplot or Tableau, that generates complete Vega specifications.

Vega-lite specifications consist of simple mappings of variables in a data set to visual encoding channels such as position (x,y), size, color and shape. These mappings are then translated into full visualization specifications using the Vega visualization grammar. These resulting visualizations can then be exported or further modified to customize the display.

Use Vega-lite in the online editor.

If you are using Vega-lite for your project(s), please let us know by emailing us at Vega-lite [at] cs.washington.edu. Feedbacks are also welcomed. If you find a bug or have a feature request, please create an issue.

The complete schema for specifications as JSON schema is at spec.json.

Example specification

Barleys

{
  "data": {"url": "data/barley.json"},
  "marktype": "point",
  "encoding": {
    "x": {"type": "Q","name": "yield","aggregate": "avg"},
    "y": {
      "sort": [{"name": "yield","aggregate": "avg","reverse": false}],
      "type": "O",
      "name": "variety"
    },
    "row": {"type": "O","name": "site"},
    "color": {"type": "O","name": "year"}
  }
}

Simple bar chart

This is a similar chart as one of the Vega examples in https://github.com/trifacta/vega/wiki/Tutorial. See how much simpler it is.

{
  "data": {
    "values": [
      {"x":"A", "y":28}, {"x":"B", "y":55}, {"x":"C", "y":43},
      {"x":"D", "y":91}, {"x":"E", "y":81}, {"x":"F", "y":53},
      {"x":"G", "y":19}, {"x":"H", "y":87}, {"x":"I", "y":52}
    ]
  },
  "marktype": "bar",
  "encoding": {
    "y": {"type": "Q","name": "y"},
    "x": {"type": "O","name": "x"}
  }
}

Setup Instructions

Make sure you have node.js. (We recommend using homebrew and simply run brew install node.)

Install gulp globally by running

npm install -g gulp

Then install all the npm dependencies:

npm install

You can run gulp to compile vega-lite or run gulp serve to open the live vega-lite editor.

Developing Vega-lite and Datalib

Vega-lite depends on Datalib. If you plan to make changes to datalib and test Vega-lite without publishing / copying compiled datalib all the time, use npm's link function.

# first link datalib global npm
cd path/to/datalib
npm link
# then link vega-lite to datalib
cd path/to/vega-lite
npm link datalib

Now all the changes you make in Datalib are reflected in your Vega-lite automatically.