Line

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.

All point* properties can be specified as an array. If these are set to an array value, the first value applies to the first point, the second value to the second point, and so on.

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.

The following values are supported for steppedLine:

• true: Step-before Interpolation (eq. 'before')
• 'before': Step-before Interpolation
• 'after': Step-after Interpolation
  If the steppedLine value is set to anything other than false, lineTension will be ignored.

Configuration 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:

Data Structure

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

When the data array is an array of numbers, the x axis is generally a . 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.

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.

High Performance Line Charts

Data Decimation

Decimating your data will achieve the best results. When there is a lot of data to display on the graph, it doesn't make sense to show tens of thousands of data points on a graph that is only a few hundred pixels wide.

There are many approaches to data decimation and selection of an algorithm will depend on your data and the results you want to achieve. For instance, decimation will preserve peaks in your data but could require up to 4 points for each pixel. This type of decimation would work well for a very noisy signal where you need to see data peaks.

If you are drawing lines on your chart, disabling bezier curves will improve render times since drawing a straight line is more performant than a bezier curve.

To disable bezier curves for an entire chart:

new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        elements: {
            line: {
            }
        }
    }
});

Disable Line Drawing

If you have a lot of data points, it can be more performant to disable rendering of the line for a dataset and only draw points. Doing this means that there is less to draw on the canvas which will improve render performance.

To disable lines:

Disable Animations

To disable animations

new Chart(ctx, {
    type: 'line',
    data: data,
    options: {
        animation: {
            duration: 0, // general animation time
        },
        hover: {
            animationDuration: 0, // duration of animations when hovering an item
        },
        responsiveAnimationDuration: 0, // animation duration after a resize
    }