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Filename : 01-Line-Chart.md
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---
title: Line Chart
anchor: line-chart
---
###Introduction
A line chart is a way of plotting data points on a line.

Often, it is used to show trend data, and the comparison of two data sets.

<div class="canvas-holder">
	<canvas width="250" height="125"></canvas>
</div>

###Example usage
```javascript
var myLineChart = new Chart(ctx).Line(data, options);
```
###Data structure

```javascript
var data = {
	labels: ["January", "February", "March", "April", "May", "June", "July"],
	datasets: [
		{
			label: "My First dataset",
			fillColor: "rgba(220,220,220,0.2)",
			strokeColor: "rgba(220,220,220,1)",
			pointColor: "rgba(220,220,220,1)",
			pointStrokeColor: "#fff",
			pointHighlightFill: "#fff",
			pointHighlightStroke: "rgba(220,220,220,1)",
			data: [65, 59, 80, 81, 56, 55, 40]
		},
		{
			label: "My Second dataset",
			fillColor: "rgba(151,187,205,0.2)",
			strokeColor: "rgba(151,187,205,1)",
			pointColor: "rgba(151,187,205,1)",
			pointStrokeColor: "#fff",
			pointHighlightFill: "#fff",
			pointHighlightStroke: "rgba(151,187,205,1)",
			data: [28, 48, 40, 19, 86, 27, 90]
		}
	]
};
```

The line chart requires an array of labels for each of the data points. This is shown on the X axis.
The data for line charts is broken up into an array of datasets. Each dataset has a colour for the fill, a colour for the line and colours for the points and strokes of the points. These colours are strings just like CSS. You can use RGBA, RGB, HEX or HSL notation.

The label key on each dataset is optional, and can be used when generating a scale for the chart.

### Chart options

These are the customisation options specific to Line charts. These options are merged with the [global chart configuration options](#getting-started-global-chart-configuration), and form the options of the chart.

```javascript
{

	///Boolean - Whether grid lines are shown across the chart
	scaleShowGridLines : true,

	//String - Colour of the grid lines
	scaleGridLineColor : "rgba(0,0,0,.05)",

	//Number - Width of the grid lines
	scaleGridLineWidth : 1,

	//Boolean - Whether to show horizontal lines (except X axis)
	scaleShowHorizontalLines: true,

	//Boolean - Whether to show vertical lines (except Y axis)
	scaleShowVerticalLines: true,

	//Boolean - Whether the line is curved between points
	bezierCurve : true,

	//Number - Tension of the bezier curve between points
	bezierCurveTension : 0.4,

	//Boolean - Whether to show a dot for each point
	pointDot : true,

	//Number - Radius of each point dot in pixels
	pointDotRadius : 4,

	//Number - Pixel width of point dot stroke
	pointDotStrokeWidth : 1,

	//Number - amount extra to add to the radius to cater for hit detection outside the drawn point
	pointHitDetectionRadius : 20,

	//Boolean - Whether to show a stroke for datasets
	datasetStroke : true,

	//Number - Pixel width of dataset stroke
	datasetStrokeWidth : 2,

	//Boolean - Whether to fill the dataset with a colour
	datasetFill : true,
	{% raw %}
	//String - A legend template
	legendTemplate : "<ul class=\"<%=name.toLowerCase()%>-legend\"><% for (var i=0; i<datasets.length; i++){%><li><span style=\"background-color:<%=datasets[i].strokeColor%>\"></span><%if(datasets[i].label){%><%=datasets[i].label%><%}%></li><%}%></ul>"
	{% endraw %}
};
```

You can override these for your `Chart` instance by passing a second argument into the `Line` method as an object with the keys you want to override.

For example, we could have a line chart without bezier curves between points by doing the following:

```javascript
new Chart(ctx).Line(data, {
	bezierCurve: false
});
// This will create a chart with all of the default options, merged from the global config,
// and the Line chart defaults, but this particular instance will have `bezierCurve` set to false.
```

We can also change these defaults values for each Line type that is created, this object is available at `Chart.defaults.Line`.


### Prototype methods

#### .getPointsAtEvent( event )

Calling `getPointsAtEvent(event)` on your Chart instance passing an argument of an event, or jQuery event, will return the point elements that are at that the same position of that event.

```javascript
canvas.onclick = function(evt){
	var activePoints = myLineChart.getPointsAtEvent(evt);
	// => activePoints is an array of points on the canvas that are at the same position as the click event.
};
```

This functionality may be useful for implementing DOM based tooltips, or triggering custom behaviour in your application.

#### .update( )

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.

```javascript
myLineChart.datasets[0].points[2].value = 50;
// Would update the first dataset's value of 'March' to be 50
myLineChart.update();
// Calling update now animates the position of March from 90 to 50.
```

#### .addData( valuesArray, label )

Calling `addData(valuesArray, label)` on your Chart instance passing an array of values for each dataset, along with a label for those points.

```javascript
// The values array passed into addData should be one for each dataset in the chart
myLineChart.addData([40, 60], "August");
// This new data will now animate at the end of the chart.
```

#### .removeData( )

Calling `removeData()` on your Chart instance will remove the first value for all datasets on the chart.

```javascript
myLineChart.removeData();
// The chart will remove the first point and animate other points into place
```