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177 lines
5.9 KiB
Markdown
177 lines
5.9 KiB
Markdown
---
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title: Bar Chart
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anchor: bar-chart
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---
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### Introduction
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A bar chart is a way of showing data as bars.
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It is sometimes used to show trend data, and the comparison of multiple data sets side by side.
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<div class="canvas-holder">
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<canvas width="250" height="125"></canvas>
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</div>
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### Example usage
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```javascript
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var myBarChart = new Chart(ctx,{
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type: 'bar',
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data: data,
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options: options
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});
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```
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### Data structure
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```javascript
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var data = {
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labels: ["January", "February", "March", "April", "May", "June", "July"],
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datasets: [
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{
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label: "My First dataset",
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// The properties below allow an array to be specified to change the value of the item at the given index
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// String or array - the bar color
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backgroundColor: "rgba(220,220,220,0.2)",
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// String or array - bar stroke color
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borderColor: "rgba(220,220,220,1)",
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// Number or array - bar border width
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borderWidth: 1,
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// String or array - fill color when hovered
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hoverBackgroundColor: "rgba(220,220,220,0.2)",
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// String or array - border color when hovered
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hoverBorderColor: "rgba(220,220,220,1)",
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// The actual data
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data: [65, 59, 80, 81, 56, 55, 40],
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// String - If specified, binds the dataset to a certain y-axis. If not specified, the first y-axis is used.
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yAxisID: "y-axis-1",
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},
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{
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label: "My Second dataset",
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backgroundColor: "rgba(220,220,220,0.2)",
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borderColor: "rgba(220,220,220,1)",
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borderWidth: 1,
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hoverBackgroundColor: "rgba(220,220,220,0.2)",
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hoverBorderColor: "rgba(220,220,220,1)",
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data: [28, 48, 40, 19, 86, 27, 90]
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}
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]
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};
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```
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The bar chart has the a very similar data structure to the line chart, and has an array of datasets, each with colours and an array of data. Again, colours are in CSS format.
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We have an array of labels too for display. In the example, we are showing the same data as the previous line chart example.
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The label key on each dataset is optional, and can be used when generating a scale for the chart.
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### Chart Options
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These are the customisation options specific to Bar charts. These options are merged with the [global chart configuration options](#getting-started-global-chart-configuration), and form the options of the chart.
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The default options for bar chart are defined in `Chart.defaults.Bar`.
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Name | Type | Default | Description
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--- |:---:| --- | ---
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stacked | Boolean | false |
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*hover*.mode | String | "label" | Label's hover mode. "label" is used since the x axis displays data by the index in the dataset.
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scales | Array | - | -
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*scales*.xAxes | Array | | The bar chart officially supports only 1 x-axis but uses an array to keep the API consistent. Use a scatter chart if you need multiple x axes.
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*Options for xAxes* | | |
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type | String | "Category" |
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display | Boolean | true | If true, show the scale.
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position | String | "bottom" | Position of the scale. Options are "top" and "bottom" for dataset scales.
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id | String | "x-axis-1" | Id of the axis so that data can bind to it
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categoryPercentage | Number | 0.8 | Specific to bar chart.
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barPercentage | Number | 0.9 |
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gridLines | Array | [See Scales](#scales). |
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*gridLines*.offsetGridLines | Boolean | true |
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scaleLabel | Array | [See Scales](#scales). |
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ticks | Array | [See Scales](#scales). |
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| | |
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*scales*.yAxes | Array | `[{ type: "linear" }]` |
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*Options for xAxes* | | |
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type | String | "linear" |
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display | Boolean | true | If true, show the scale.
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position | String | "left" | Position of the scale. Options are "left" and "right" for dataset scales.
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id | String | "y-axis-1" | Id of the axis so that data can bind to it
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gridLines | Array | [See Scales](#scales) |
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scaleLabel | Array | [See Scales](#scales) |
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ticks | Array | [See Scales](#scales) |
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You can override these for your `Chart` instance by passing a second argument into the `Bar` method as an object with the keys you want to override.
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For example, we could have a bar chart without a stroke on each bar by doing the following:
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```javascript
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new Chart(ctx,{
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type:"bar",
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data: data,
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options: {
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scales: {
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xAxes: [{
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stacked: true,
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}],
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yAxes: [{
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stacked: true
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}]
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}
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}
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}
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});
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// This will create a chart with all of the default options, merged from the global config,
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// and the Bar chart defaults but this particular instance will have `stacked` set to true for
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// both x and y axes.
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```
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We can also change these defaults values for each Bar type that is created, this object is available at `Chart.defaults.Bar`.
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### Prototype methods
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#### .getBarsAtEvent( event )
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Calling `getBarsAtEvent(event)` on your Chart instance passing an argument of an event, or jQuery event, will return the bar elements that are at that the same position of that event.
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```javascript
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canvas.onclick = function(evt){
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var activeBars = myBarChart.getBarsAtEvent(evt);
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// => activeBars is an array of bars on the canvas that are at the same position as the click event.
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};
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```
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This functionality may be useful for implementing DOM based tooltips, or triggering custom behaviour in your application.
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#### .update( )
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Calling `update()` on your Chart instance will re-render the chart with any updated values, allowing you to edit the value of multiple existing points, then render those in one animated render loop.
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```javascript
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myBarChart.datasets[0].bars[2].value = 50;
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// Would update the first dataset's value of 'March' to be 50
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myBarChart.update();
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// Calling update now animates the position of March from 90 to 50.
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```
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#### .addData( valuesArray, label )
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Calling `addData(valuesArray, label)` on your Chart instance passing an array of values for each dataset, along with a label for those bars.
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```javascript
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// The values array passed into addData should be one for each dataset in the chart
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myBarChart.addData([40, 60], "August");
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// The new data will now animate at the end of the chart.
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```
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#### .removeData( )
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Calling `removeData()` on your Chart instance will remove the first value for all datasets on the chart.
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```javascript
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myBarChart.removeData();
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// The chart will now animate and remove the first bar
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```
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