ChartJS - Different color per data point

Question

Is there a way to set a different color to a datapoint in a Line Chart if its above a certain value?

I found this example for dxChart - https://stackoverflow.com/a/2

Answer 1

With recent versions of chart.js I would recommend doing this with scriptable options.

Scriptable options give you an easy way to vary the style of a dataset property (e.g. line point colour) dynamically according to some function you provide. This is passed a 'context' object that tells it the index and value of the point etc. (see below).

Most chart properties can be scripted; the dataset properties for each chart type tell you the exact list (e.g. see here for line chart).

Here is how you might use scriptable options on a line chart (based on the example in the docs). On this chart negative data points are shown in red, and positive ones in alternating blue/green:

window.myChart = Chart.Line(ctx, {
    data: {
        labels: x_data,
        datasets: [
            {
                data: y_data,
                label: "Test Data",
                borderColor: "#3e95cd",
                fill: false,
                pointBackgroundColor: function(context) {
                    var index = context.dataIndex;
                    var value = context.dataset.data[index];
                    return value < 0 ? 'red' :  // draw negative values in red
                        index % 2 ? 'blue' :    // else, alternate values in blue and green
                            'green';
                }
            }
        ],
    }
});

The context object passed to your function can have the following properties. Some of these won't be present for certain types of entity, so test before use.

• chart: the associated chart
• dataIndex: index of the current data
• dataset: dataset at index datasetIndex
• datasetIndex: index of the current dataset
• hover: true if hovered