line.md

Line

A line chart is a way of plotting data points on a line. Often, it is used to show trend data, or the comparison of two data sets.

{% chartjs %} { "type": "line", "data": { "labels": [ "January", "February", "March", "April", "May", "June", "July" ], "datasets": [{ "label": "My First Dataset", "data": [65, 59, 80, 81, 56, 55, 40], "fill": false, "borderColor": "rgb(75, 192, 192)", "lineTension": 0.1 }] }, "options": {

}

} {% endchartjs %}

Example Usage

var myLineChart = new Chart(ctx, {
    type: 'line',
    data: data,
    options: options
});

Dataset Properties

The line chart allows a number of properties to be specified for each dataset. These are used to set display properties for a specific dataset. For example, the colour of a line is generally set this way.

Name	Type	Scriptable	Indexable	Default
backgroundColor	Color	Yes	-	'rgba(0, 0, 0, 0.1)'
borderCapStyle	string	Yes	-	'butt'
borderColor	Color	Yes	-	'rgba(0, 0, 0, 0.1)'
borderDash	number[]	Yes	-	[]
borderDashOffset	number	Yes	-	0.0
borderJoinStyle	string	Yes	-	'miter'
borderWidth	number	Yes	-	3
cubicInterpolationMode	string	Yes	-	'default'
fill	boolean|string	Yes	-	true
hoverBackgroundColor	Color	Yes	-	undefined
hoverBorderCapStyle	string	Yes	-	undefined
hoverBorderColor	Color	Yes	-	undefined
hoverBorderDash	number[]	Yes	-	undefined
hoverBorderDashOffset	number	Yes	-	undefined
hoverBorderJoinStyle	string	Yes	-	undefined
hoverBorderWidth	number	Yes	-	undefined
label	string	-	-	''
lineTension	number	-	-	0.4
order	number	-	-	0
pointBackgroundColor	Color	Yes	Yes	'rgba(0, 0, 0, 0.1)'
pointBorderColor	Color	Yes	Yes	'rgba(0, 0, 0, 0.1)'
pointBorderWidth	number	Yes	Yes	1
pointHitRadius	number	Yes	Yes	1
pointHoverBackgroundColor	Color	Yes	Yes	undefined
pointHoverBorderColor	Color	Yes	Yes	undefined
pointHoverBorderWidth	number	Yes	Yes	1
pointHoverRadius	number	Yes	Yes	4
pointRadius	number	Yes	Yes	3
pointRotation	number	Yes	Yes	0
pointStyle	string|Image	Yes	Yes	'circle'
showLine	boolean	-	-	undefined
spanGaps	boolean	-	-	undefined
steppedLine	boolean|string	-	-	false
xAxisID	string	-	-	first x axis
yAxisID	string	-	-	first y axis

General

Name	Description
label	The label for the dataset which appears in the legend and tooltips.
order	The drawing order of dataset. Also affects order for stacking, tooltip, and legend.
xAxisID	The ID of the x axis to plot this dataset on.
yAxisID	The ID of the y axis to plot this dataset on.

Point Styling

The style of each point can be controlled with the following properties:

Name	Description
pointBackgroundColor	The fill color for points.
pointBorderColor	The border color for points.
pointBorderWidth	The width of the point border in pixels.
pointHitRadius	The pixel size of the non-displayed point that reacts to mouse events.
pointRadius	The radius of the point shape. If set to 0, the point is not rendered.
pointRotation	The rotation of the point in degrees.
pointStyle	Style of the point. more...

All these values, if undefined, fallback first to the dataset options then to the associated elements.point.* options.

Line Styling

The style of the line can be controlled with the following properties:

Name	Description
backgroundColor	The line fill color.
borderCapStyle	Cap style of the line. See MDN.
borderColor	The line color.
borderDash	Length and spacing of dashes. See MDN.
borderDashOffset	Offset for line dashes. See MDN.
borderJoinStyle	Line joint style. See MDN.
borderWidth	The line width (in pixels).
fill	How to fill the area under the line. See area charts.
lineTension	Bezier curve tension of the line. Set to 0 to draw straightlines. This option is ignored if monotone cubic interpolation is used.
showLine	If false, the line is not drawn for this dataset.
spanGaps	If true, lines will be drawn between points with no or null data. If false, points with NaN data will create a break in the line.

If the value is undefined, showLine and spanGaps fallback to the associated chart configuration options. The rest of the values fallback to the associated elements.line.* options.

Interactions

The interaction with each point can be controlled with the following properties:

Name	Description
pointHoverBackgroundColor	Point background color when hovered.
pointHoverBorderColor	Point border color when hovered.
pointHoverBorderWidth	Border width of point when hovered.
pointHoverRadius	The radius of the point when hovered.

cubicInterpolationMode

The following interpolation modes are supported.

• 'default'
• 'monotone'

The 'default' algorithm uses a custom weighted cubic interpolation, which produces pleasant curves for all types of datasets.

The 'monotone' algorithm is more suited to y = f(x) datasets : it preserves monotonicity (or piecewise monotonicity) of the dataset being interpolated, and ensures local extremums (if any) stay at input data points.

If left untouched (undefined), the global options.elements.line.cubicInterpolationMode property is used.

Stepped Line

The following values are supported for steppedLine.

• false: No Step Interpolation (default)
• true: Step-before Interpolation (eq. 'before')
• 'before': Step-before Interpolation
• 'after': Step-after Interpolation
• 'middle': Step-middle Interpolation

If the steppedLine value is set to anything other than false, lineTension will be ignored.

Configuration Options

The line chart defines the following configuration options. These options are merged with the global chart configuration options, Chart.defaults.global, to form the options passed to the chart.

Name	Type	Default	Description
showLines	boolean	true	If false, the lines between points are not drawn.
spanGaps	boolean	false	If false, NaN data causes a break in the line.

Default Options

It is common to want to apply a configuration setting to all created line charts. The global line chart settings are stored in Chart.defaults.line. Changing the global options only affects charts created after the change. Existing charts are not changed.

For example, to configure all line charts with spanGaps = true you would do:

Chart.defaults.line.spanGaps = true;

Data Structure

The data property of a dataset for a line chart can be passed in two formats.

number[]

data: [20, 10]

When the data array is an array of numbers, the x axis is generally a category. The points are placed onto the axis using their position in the array. When a line chart is created with a category axis, the labels property of the data object must be specified.

Point[]

data: [{
    x: 10,
    y: 20
}, {
    x: 15,
    y: 10
}]

This alternate is used for sparse datasets, such as those in scatter charts. Each data point is specified using an object containing x and y properties.

Stacked Area Chart

Line charts can be configured into stacked area charts by changing the settings on the y axis to enable stacking. Stacked area charts can be used to show how one data trend is made up of a number of smaller pieces.

var stackedLine = new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        scales: {
            yAxes: [{
                stacked: true
            }]
        }
    }
});