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61 lines
2.5 KiB
Markdown
61 lines
2.5 KiB
Markdown
# Labeling Axes
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When creating a chart, you want to tell the viewer what data they are viewing. To do this, you need to label the axis.
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## Scale Title Configuration
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Namespace: `options.scales[scaleId].title`, it defines options for the scale title. Note that this only applies to cartesian axes.
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| Name | Type | Default | Description
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| ---- | ---- | ------- | -----------
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| `display` | `boolean` | `false` | If true, display the axis title.
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| `align` | `string` | `'center'` | Alignment of the axis title. Possible options are `'start'`, `'center'` and `'end'`
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| `text` | `string`\|`string[]` | `''` | The text for the title. (i.e. "# of People" or "Response Choices").
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| `color` | [`Color`](../general/colors.md) | `Chart.defaults.color` | Color of label.
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| `font` | `Font` | `Chart.defaults.font` | See [Fonts](../general/fonts.md)
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| `padding` | [`Padding`](../general/padding.md) | `4` | Padding to apply around scale labels. Only `top` and `bottom` are implemented.
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## Creating Custom Tick Formats
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It is also common to want to change the tick marks to include information about the data type. For example, adding a dollar sign ('$').
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To do this, you need to override the `ticks.callback` method in the axis configuration.
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The method receives 3 arguments:
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* `value` - the tick value in the **internal data format** of the associated scale.
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* `index` - the tick index in the ticks array.
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* `ticks` - the array containing all of the [tick objects](../api/interfaces/Tick).
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The call to the method is scoped to the scale. `this` inside the method is the scale object.
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If the callback returns `null` or `undefined` the associated grid line will be hidden.
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:::tip
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The [category axis](../axes/cartesian/category), which is the default x-axis for line and bar charts, uses the `index` as internal data format. For accessing the label, use `this.getLabelForValue(value)`. [API: getLabelForValue](../api/classes/scale.html#getlabelforvalue)
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:::
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In the following example, every label of the Y-axis would be displayed with a dollar sign at the front.
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```javascript
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var chart = new Chart(ctx, {
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type: 'line',
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data: data,
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options: {
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scales: {
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y: {
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ticks: {
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// Include a dollar sign in the ticks
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callback: function(value, index, values) {
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return '$' + value;
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}
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}
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}
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}
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}
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});
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```
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Related samples:
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* [Tick configuration sample](../samples/scale-options/ticks)
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