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.

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.

General

Point Styling

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

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:

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:

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.

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
            }]
        }
    }
});