76 lines
3.3 KiB
Markdown
76 lines
3.3 KiB
Markdown
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# Linear Cartesian Axis
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The linear scale is use to chart numerical data. It can be placed on either the x or y axis. The scatter chart type automatically configures a line chart to use one of these scales for the x axis. As the name suggests, linear interpolation is used to determine where a value lies on the axis.
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## Tick Configuration Options
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The following options are provided by the linear scale. They are all located in the `ticks` sub options. These options extend the [common tick configuration](README.md#tick-configuration).
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| Name | Type | Default | Description
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| ---- | ---- | ------- | -----------
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| `beginAtZero` | `boolean` | | if true, scale will include 0 if it is not already included.
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| `min` | `number` | | User defined minimum number for the scale, overrides minimum value from data. [more...](#axis-range-settings)
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| `max` | `number` | | User defined maximum number for the scale, overrides maximum value from data. [more...](#axis-range-settings)
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| `maxTicksLimit` | `number` | `11` | Maximum number of ticks and gridlines to show.
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| `precision` | `number` | | if defined and `stepSize` is not specified, the step size will be rounded to this many decimal places.
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| `stepSize` | `number` | | User defined fixed step size for the scale. [more...](#step-size)
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| `suggestedMax` | `number` | | Adjustment used when calculating the maximum data value. [more...](#axis-range-settings)
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| `suggestedMin` | `number` | | Adjustment used when calculating the minimum data value. [more...](#axis-range-settings)
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## Axis Range Settings
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Given the number of axis range settings, it is important to understand how they all interact with each other.
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The `suggestedMax` and `suggestedMin` settings only change the data values that are used to scale the axis. These are useful for extending the range of the axis while maintaining the auto fit behaviour.
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```javascript
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let minDataValue = Math.min(mostNegativeValue, options.ticks.suggestedMin);
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let maxDataValue = Math.max(mostPositiveValue, options.ticks.suggestedMax);
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```
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In this example, the largest positive value is 50, but the data maximum is expanded out to 100. However, because the lowest data value is below the `suggestedMin` setting, it is ignored.
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```javascript
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let chart = new Chart(ctx, {
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type: 'line',
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data: {
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datasets: [{
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label: 'First dataset',
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data: [0, 20, 40, 50]
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}],
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labels: ['January', 'February', 'March', 'April']
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},
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options: {
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scales: {
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yAxes: [{
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ticks: {
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suggestedMin: 50,
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suggestedMax: 100
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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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In contrast to the `suggested*` settings, the `min` and `max` settings set explicit ends to the axes. When these are set, some data points may not be visible.
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## Step Size
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If set, the scale ticks will be enumerated by multiple of `stepSize`, having one tick per increment. If not set, the ticks are labeled automatically using the nice numbers algorithm.
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This example sets up a chart with a y axis that creates ticks at `0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5`.
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```javascript
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let options = {
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scales: {
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yAxes: [{
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ticks: {
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max: 5,
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min: 0,
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stepSize: 0.5
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}
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}]
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}
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};
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```
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