G2

In G2, encoding is mainly used to specify the relationship between visual element attributes and data. You can specify encoding at the mark level:

({
  type: 'interval',
  encode: {
    x: 'name',
    y: 'value',
  },
});

// API
// First kind
chart.interval().encode('x', 'name').encode('y', 'value');

// Second kind
chart.interval().encode({ x: 'name', y: 'value' });

You can also specify encoding at the view level:

({
  type: 'view',
  encode: {
    x: 'name',
    y: 'value',
  },
});

// API
// First kind
chart.encode('x', 'name').encode('y', 'value');

// Second kind
chart.encode({ x: 'name', y: 'value' });

Channels

To control the style of the mark, we often bind a column of data to its visual attribute. For example, in the example below, we bind the 'height' column of data to the 'x' attribute, the 'weight' column of data to the 'y' attribute, and the 'gender' column of data to the 'color' attribute.

table({
  url: 'https://gw.alipayobjects.com/os/antvdemo/assets/data/scatter.json',
});

(() => {
  const chart = new G2.Chart();

  chart
    .point()
    .data({
      type: 'fetch',
      value:
        'https://gw.alipayobjects.com/os/antvdemo/assets/data/scatter.json',
    })
    .encode('x', 'weight')
    .encode('y', 'height')
    .encode('color', 'gender');

  chart.render();

  return chart.getContainer();
})();

This binding process is called encode. We often say that a visual attribute of the graph is encoded by a column of data, and this data-driven property is called a channel. For example, the x, y, and color channels of the point mark in the example above are each encoded by the corresponding column of data.

A complete encoding consists of encode.type and encode.value:

({
  type: 'point',
  encode: {
    x: { type: 'field', value: 'weight' },
    y: { type: 'field', value: 'height' },
    color: { type: 'field', value: 'gender' },
  },
});

In most cases, you can directly specify the value, as shown below for encoding some built-in categories:

Field Encode

Specify the binding of the channel and a certain column of the data:

({
  type: 'interval',
  encode: { x: { type: 'field', value: 'name' } },
});

// Syntax sugar
({
  type: 'interval',
  encode: { x: 'name' },
});

Function Encode

Specify the binding of the channel and some newly generated bindings:

({
  type: 'interval',
  encode: {
    color: {
      type: 'transform',
      value: (d) => (d.value > 100 ? 'high' : 'low'),
    },
  },
});

// Syntax sugar
({
  type: 'interval',
  encode: {
    color: (d) => (d.value > 100 ? 'high' : 'low'),
  },
});

Constant Encode

Set the channel value to a constant, which is often used to specify the color channel.

({
  type: 'interval',
  encode: { color: { type: 'constant', value: 'steelblue' } },
});

// Syntax sugar
({
  type: 'interval',
  encode: { color: 'steelblue' },
});

Data Encode

Specify the value of a channel as an array.

({
  type: 'line',
  encode: {
    x: { type: 'column', value: [0, 1, , 2, 3] },
  },
});

For some big data scenarios, using array columns is more suitable, here is a simple example.

(() => {
  const I = [0, 1, 2, 3, 4];
  const X = I.map((i) => ((i - 2) * Math.PI) / 2);
  const Y = X.map((x) => Math.sin(x));

  const chart = new G2.Chart();

  chart
    .line()
    .data(I)
    .encode('x', { type: 'column', value: X })
    .encode('y', { type: 'column', value: Y })
    .encode('shape', 'smooth');

  chart.render();

  return chart.getContainer();
})();

Array Channels

Certainly, for spatial channels like x and y channels, you often need more than one column of data, such as a waterfall chart, you can specify multiple columns for a channel through an array.

(() => {
  const chart = new G2.Chart();

  chart
    .interval()
    .data([
      { month: 'Jan.', profit: 387264, start: 0, end: 387264 },
      { month: 'Feb.', profit: 772096, start: 387264, end: 1159360 },
      { month: 'Mar.', profit: 638075, start: 1159360, end: 1797435 },
      { month: 'Apr.', profit: -211386, start: 1797435, end: 1586049 },
      { month: 'May', profit: -138135, start: 1586049, end: 1447914 },
      { month: 'Jun', profit: -267238, start: 1447914, end: 1180676 },
      { month: 'Jul.', profit: 431406, start: 1180676, end: 1612082 },
      { month: 'Aug.', profit: 363018, start: 1612082, end: 1975100 },
      { month: 'Sep.', profit: -224638, start: 1975100, end: 1750462 },
      { month: 'Oct.', profit: -299867, start: 1750462, end: 1450595 },
      { month: 'Nov.', profit: 607365, start: 1450595, end: 2057960 },
      { month: 'Dec.', profit: 1106986, start: 2057960, end: 3164946 },
      { month: 'Total', start: 0, end: 3164946 },
    ])
    .encode('x', 'month')
    .encode('y', ['end', 'start']) // specify two columns of data
    .encode('color', (d) =>
      d.month === 'Total' ? 'Total' : d.profit > 0 ? 'Increase' : 'Decrease',
    )
    .axis('y', { labelFormatter: '~s' });

  chart.render();

  return chart.getContainer();
})();

In addition, you can specify them separately in the form of ${channel}${index}:

// Equivalent to the above form
chart.encode('y', 'end').encode('y1', 'start');

Common Channels

Different marks have different channels, but there are also some common channels. Some common and drawing-related common channels are as follows:

x - x position
y - y position
z - z position
color - color, fill color or border color, determined by shape
opacity - opacity, fill-opacity or border opacity, determined by the style
shape - shape
size - size, different marks have different functions
series - series, used to split into series
key - unique mark, used for data updates

View Encode

Channel encode has transitivity, the encoding of the view is passed to the mark specified by children, if the mark does not have the encoding of the corresponding channel, then set, otherwise do nothing. For example, draw a point line chart:

(() => {
  const chart = new G2.Chart();

  chart
    .data([
      { year: '1991', value: 3 },
      { year: '1992', value: 4 },
      { year: '1993', value: 3.5 },
      { year: '1994', value: 5 },
      { year: '1995', value: 4.9 },
      { year: '1996', value: 6 },
      { year: '1997', value: 7 },
      { year: '1998', value: 9 },
      { year: '1999', value: 13 },
    ])
    .encode('x', 'year') // View level encoding
    .encode('y', 'value');

  chart.line();

  chart.point();

  chart.render();

  return chart.getContainer();
})();