Line chart

(quoted from Line chart definition in Wikipedia)

A line chart is a type of chart which displays information as a series of data or data points connected by straight line segments. It is a basic type of chart common in many fields. The measurement points are ordered (typically by their x-axis value) and joined with straight line segments. A line chart is often used to visualize a trend in data over intervals of time, a time series, thus the line is often drawn chronologically.

Programmatically, you could use a line chart as following:

// creates the chart    
LineChart chart = new LineChart();
// adds to DOM
component.add(chart);
...
// example for Elemental2
// gets the chart instance as DOM element
Element element = chart.getChartElement().as();
// adds to DOM
DomGlobal.document.body.appendChild(element);

By UIBinder (ONLY for GWT), you could use a line chart as following:

<ui:UiBinder xmlns:ui="urn:ui:com.google.gwt.uibinder"
   xmlns:g="urn:import:com.google.gwt.user.client.ui"
   xmlns:c="urn:import:org.pepstock.charba.client.gwt.widgets">

   <g:HTMLPanel  width="100%">
      ....
      <c:LineChartWidget ui:field="chart"/>
      ...
   </g:HTMLPanel>
</ui:UiBinder> 

Dataset

The line chart allows to define the data and a number of properties, used to display the data, by a line dataset.

Every chart has got a method to create a typed dataset accordingly with the chart type. The dataset can be also created instantiating the constructor.

// creates the chart
LineChart chart = new LineChart();
// creates the dataset
LineDataset dataset = chart.newDataset();
// sets the option
dataset.setBackgroundColor(HtmlColor.RED);
...
// creates the dataset
LineDataset datasetNew = new LineDataset();
// sets the option
datasetNew.setBackgroundColor(HtmlColor.RED);
...
// sets the datasets to the chart
chart.getData().setDatasets(dataset, datasetNew);

The following are the attributes that you can set:

Name	Type	Scriptable	Description
backgroundColor	String - IsColor - Pattern - Gradient	Yes	The fill color/pattern under the line.
borderCapStyle	CapStyle	Yes	Cap style of the line. See MDN.
borderColor	String - IsColor - Gradient	Yes	The color of the line.
borderDash	int[]	Yes	Length and spacing of dashes. See MDN.
borderDashOffset	double	Yes	Offset for line dashes. See MDN.
borderJoinStyle	JoinStyle	Yes	Line joint style. See MDN.
borderWidth	int	Yes	The width of the line in pixels.
cubicInterpolationMode	CubicInterpolationMode	Yes	Algorithm used to interpolate a smooth curve from the discrete data points.
clip	boolean - double - Clip	-	How to clip relative to chart area. Positive value allows overflow, negative value clips that many pixels inside chart area.
drawActiveElementsOnTop	boolean	Yes	Draw the active points of a dataset over the other points of the dataset.
fill	String - int - boolean - IsFill	Yes	How to fill the area under the line. See Filling modes.
hoverBackgroundColor	String - IsColor - Pattern - Gradient	Yes	The fill color/pattern under the line, when hovered.
hoverBorderCapStyle	CapStyle	Yes	Cap style of the line, when hovered. See MDN.
hoverBorderColor	String - IsColor - Gradient	Yes	The color of the line, when hovered.
hoverBorderDash	int[]	Yes	Length and spacing of dashes, when hovered. See MDN.
hoverBorderDashOffset	int	Yes	Offset for line dashes, when hovered. See MDN.
hoverBorderJoinStyle	JoinStyle	Yes	Line joint style, when hovered. See MDN.
hoverBorderWidth	int	Yes	The width of the line in pixels, when hovered.
indexAxis	IndexAxis	-	The base axis of the dataset. 'IndexAxis.X' for horizontal lines and 'IndexAxis.Y' for vertical lines.
label	String	-	The label for the dataset which appears in the legend and tooltips.
normalized	boolean	-	If true, you provide data with indices that are unique, sorted, and consistent across data sets and provide the normalized.
order	int	-	The drawing order of dataset. Also affects order for stacking, tooltip, and legend.
parsing	boolean	-	If false, the data set parsing is disable. If parsing is disabled, data must be sorted and in the formats the associated chart type and scales use internally.
pointBackgroundColor	String[] - IsColor[] - Gradient[]	Yes	The fill color for points.
pointBorderColor	String[] - IsColor[] - Gradient[]	Yes	The border color for points.
pointBorderWidth	int[]	Yes	The width of the point border in pixels.
pointHitRadius	double[]	Yes	The pixel size of the non-displayed point that reacts to mouse events.
pointHoverBackgroundColor	String[] - IsColor[] - Gradient[]	Yes	Point background color when hovered.
pointHoverBorderColor	String[] - IsColor[] - Gradient[]	Yes	Point border color when hovered.
pointHoverBorderWidth	int[]	Yes	Border width of point when hovered.
pointHoverRadius	double[]	Yes	The radius of the point when hovered.
pointRadius	double[]	Yes	The radius of the point shape. If set to 0, the point is not rendered.
pointRotation	double[]	Yes	The rotation of the point in degrees.
pointStyle	PointStyle[] - Img[] - Canvas[]	Yes	Style of the point.
showLine	boolean	-	If false, the line is not drawn for this dataset.
spanGaps	boolean - double	-	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. Can also be a number specifying the maximum gap length to span. The unit of the value depends on the scale used.
stepped	boolean - Stepped	Yes	If the line is shown as a stepped line.
tension	double	-	Bezier curve tension of the line. Set to 0 to draw straight lines. This option is ignored if monotone cubic interpolation is used.
xAxisID	String	-	The ID of the x axis to plot this dataset on.
yAxisID	String	-	The ID of the y axis to plot this dataset on.

General

The general options for a line dataset can control behaviors not related to styling or interactions and they are the following:

Name	Defaults	Description
clip	Undefined.DOUBLE	How to clip relative to chart area.
drawActiveElementsOnTop	true	Draw the active points of a dataset over the other points of the dataset.
indexAxis	IndexAxis.X	The base axis of the dataset.
label	null	The label for the dataset which appears in the legend and tooltips.
normalized	false	If true, you provide data with indices that are unique, sorted, and consistent across data sets and provide the normalized.
order	0	The drawing order of dataset. Also affects order for stacking, tooltip, and legend.
parsing	true	If false, the data set parsing is disable. If parsing is disabled, data must be sorted and in the formats the associated chart type and scales use internally.
xAxisID	DefaultScaleId.X	The ID of the x axis to plot this dataset on.
yAxisID	DefaultScaleId.Y	The ID of the y axis to plot this dataset on.

Point styling

The style of each point of the dataset can be configured by 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.
pointRotation	The rotation of the point in degrees.
pointStyle	Style of the point.

All above options have got the fallback to the associated Point elements, retrievable by the following statements:

// from chart instance
Point point = chart.getOptions().getElements().getPoint();
// sets options for all line datasets of the chart
point.setRadius(6);
...
// from defaults
Point defaultPoint  = Defaults.get().getGlobal().getElements().getPoint();
// sets options for all line datasets of all charts
defaultPoint.setRadius(6);

Line styling

The style of each line of the dataset can be configured by the following properties:

Name	Description
backgroundColor	The fill color under the line.
borderCapStyle	Cap style of the line.
borderColor	The color of the line.
borderDash	Length and spacing of dashes.
borderDashOffset	Offset for line dashes.
borderJoinStyle	Line joint style
borderWidth	The width of the line in pixels.
cubicInterpolationMode	Algorithm used to interpolate a smooth curve from the discrete data points.
fill	How to fill the area under the line.
stepped	If the line is shown as a stepped line.
tension	Bezier curve tension of the line.

All above options have got the fallback to the associated Line elements, retrievable by the following statements:

// from chart instance
Line line = chart.getOptions().getElements().getLine();
// sets options for all line datasets of the chart
line.setBorderWidth(6);
...
// from defaults
Line defaultLine  = Defaults.get().getGlobal().getElements().getLine();
// sets options for all line datasets of all charts
defaultLine.setBorderWidth(6);

Point 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.

All above options have got the fallback to the associated Point elements, retrievable by the following statements:

// from chart instance
Point point = chart.getOptions().getElements().getPoint();
// sets options for all line datasets of the chart
point.setRadius(6);
...
// from defaults
Point defaultPoint  = Defaults.get().getGlobal().getElements().getPoint();
// sets options for all line datasets of all charts
defaultPoint.setRadius(6);

Line interactions

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

Name	Description
hoverBackgroundColor	The fill color under the line, when hovered.
hoverBorderCapStyle	Cap style of the line, when hovered.
hoverBorderColor	The color of the line, when hovered.
hoverBorderDash	Length and spacing of dashes, when hovered.
hoverBorderDashOffset	Offset for line dashes, when hovered.
hoverBorderJoinStyle	Line joint style, when hovered.
hoverBorderWidth	The width of the line in pixels, when hovered.

All above options have got the fallback to the associated Line elements, retrievable by the following statements:

// from chart instance
Line line = chart.getOptions().getElements().getLine();
// sets options for all line datasets of the chart
line.setBorderWidth(6);
...
// from defaults
Line defaultLine  = Defaults.get().getGlobal().getElements().getLine();
// sets options for all line datasets of all charts
defaultLine.setBorderWidth(6);

Scriptable

Scriptable options at dataset level accept a callback which is called for each of the underlying data values. See more details in Configuring charts section.

// creates chart
LineChart chart = new LineChart();
// creates dataset
LineDataset dataset = chart.newDataset();
// sets the option by a callback 
dataset.setBackgroundColor(new ColorCallback<DatasetContext>(){

   @Override
   public IsColor invoke(DatasetContext context){
      // logic
      return color;
   }
});

The following options can be set by a callback:

Name	Callback	Returned types
backgroundColor	ColorCallback<DatasetContext>	String - IsColor - Pattern - Gradient
borderCapStyle	CapStyleCallback<DatasetContext>	CapStyle
borderColor	ColorCallback<DatasetContext>	String - IsColor - Gradient
borderDash	BorderDashCallback<DatasetContext>	List<Integer>
borderDashOffset	BorderDashOffsetCallback<DatasetContext>	double
borderJoinStyle	JoinStyleCallback<DatasetContext>	JoinStyle
borderWidth	WidthCallback<DatasetContext>	int
cubicInterpolationMode	CubicInterpolationModeCallback	CubicInterpolationMode
drawActiveElementsOnTop	DrawActiveElementsOnTopCallback	boolean
fill	FillCallback	String - int - boolean - IsFill
hoverBackgroundColor	ColorCallback<DatasetContext>	String - IsColor - Pattern - Gradient
hoverBorderCapStyle	CapStyleCallback<DatasetContext>	CapStyle
hoverBorderColor	ColorCallback<DatasetContext>	String - IsColor - Gradient
hoverBorderDash	BorderDashCallback<DatasetContext>	List<Integer>
hoverBorderDashOffset	BorderDashOffsetCallback<DatasetContext>	int
hoverBorderJoinStyle	JoinStyleCallback<DatasetContext>	JoinStyle
hoverBorderWidth	WidthCallback<DatasetContext>	int
pointBackgroundColor	ColorCallback<DatasetContext>	String - IsColor - Gradient
pointBorderColor	ColorCallback<DatasetContext>	String - IsColor - Gradient
pointBorderWidth	WidthCallback<DatasetContext>	int
pointHitRadius	RadiusCallback<DatasetContext>	double
pointHoverBackgroundColor	ColorCallback<DatasetContext>	String - IsColor - Gradient
pointHoverBorderColor	ColorCallback<DatasetContext>	String - IsColor - Gradient
pointHoverBorderWidth	WidthCallback<DatasetContext>	int
pointHoverRadius	RadiusCallback<DatasetContext>	double
pointRadius	RadiusCallback<DatasetContext>	double
pointRotation	RotationCallback<DatasetContext>	double
pointStyle	PointStyleCallback<DatasetContext>	boolean - PointStyle - Img - Canvas
stepped	SteppedCallback	Stepped

Data structure

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

Data as doubles

When the data is an array or list of doubles, 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.

// sets data as an array of doubles
dataset.setData(1,2,3,4,6);

// sets data as a list of double
List<Double> list = new LinkedList<>();
list.add(1);
list.add(2);
list.add(3);
dataset.setData(list);

Data as DataPoint

This alternate is used for sparse datasets, such as those in scatter or time series charts. Each data point is specified using an object containing x and y properties (for scatter chart) or containing y and t (as time type) properties for time series.

// creates a datapoint
DataPoint dp1 = new DataPoint();
dp1.setX(10);
dp1.setY(20);
// creates a datapoint
DataPoint dp2 = new DataPoint();
dp2.setX(30);
dp2.setY(40);
// sets data by an array of datapoints
dataset.setDataPoint(dp1, dp2);

Data as strings

You can set data of charts as an array of strings. Each point in the data array corresponds to the label at the same index on the x axis.

...
dataset.setDataString("label1", "label2");
....

Options

The line chart defines specific options implementation to be configured. These options are merged with the global chart configuration options to form the options passed to the chart.

// creates chart
LineChart chart = new LineChart();
// gets the chart options
LineOptions options = chart.getOptions();
// sets options
options.setResponsive(true);
options.setShowLine(false);

These are the options specific to line charts:

Name	Type	Default	Description
showLine	boolean	true	If false, the lines between points are not drawn.
spanGaps	boolean - double	false	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. Can also be a number specifying the maximum gap length to span. The unit of the value depends on the scale used.

Setting showLine to false:

Segment

The line charts can contain a segment options element which can manage the styles of data sets in each own segment between the points and can override the data set configuration by scriptable options.

// creates chart
LineChart chart = new LineChart();
// sets segment callback for border color
chart.getOptions().getSegment().setBorderColor(new ColorCallback<SegmentContext>() {
            
    @Override
    public Object invoke(SegmentContext context) {
        // if value of point 1 greater than value of point 0
        // the border color will be "green", otherwise "gray"
        double valuePoint0 = context.getStartPoint().getParsed().getY();
        double valuePoint1 = context.getEndPoint().getParsed().getY();
        return valuePoint0 < valuePoint1 ? HtmlColor.GRAY : HtmlColor.GREEN;
    }
});
// sets segment callback for background color
chart.getOptions().getSegment().setBackgroundColor(new ColorCallback<SegmentContext>() {
            
    @Override
    public Object invoke(SegmentContext context) {
        // if value of point 1 greater than value of point 0
        // the background color will be "light green", otherwise "gray"
        double valuePoint0 = context.getStartPoint().getParsed().getY();
        double valuePoint1 = context.getEndPoint().getParsed().getY();
        return valuePoint0 < valuePoint1 ? HtmlColor.LIGHT_GRAY : HtmlColor.LIGHT_GREEN;
    }
});

Currently all of the border options and background color are supported. The segment styles are resolved for each section of the line between each point.

These are the options specific to line charts:

Name	Callback	Returned types
backgroundColor	ColorCallback<SegmentContext>	String - IsColor - Pattern
borderCapStyle	CapStyleCallback<SegmentContext>	CapStyle
borderColor	ColorCallback<SegmentContext>	String - IsColor
borderDash	BorderDashCallback<SegmentContext>	List<Integer>
borderDashOffset	BorderDashOffsetCallback<SegmentContext>	double
borderJoinStyle	JoinStyleCallback<SegmentContext>	JoinStyle
borderWidth	WidthCallback<SegmentContext>	int

The callbacks are getting the only 1 argument, the segment context which contains the context of the callback execution.

The context object contains the following properties:

Name	Type	Description
attributes	NativeObjectContainer	User object which you can store your options at runtime.
chart	IsChart	Chart instance.
datasetIndex	int	The index of the dataset.
endDataIndex	int	The index of second point in the data.
endPoint	PointElement	The line element for the end point of the segment.
startDataIndex	int	The index of first point in the data.
startPoint	PointElement	The line element for the start point of the segment.
type	ContextType	The type of the context. It can be ONLY ContextType.SEGMENT.