Charts API

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Moodle 3.2


Overview

The Charts API is a core set of methods intended to provide a simple and yet modern interface to generate dynamic charts.

Chart types

The first step to create a new chart is to create an instance of the desired chart type. At the moment bar, line and pie types are supported and using some display changing methods can change how the charts are displayed.

Bar

To create a new bar chart, just create a new instance of chart_bar class.

$chart = new core\chart_bar();
$chart->add_series($sales);
$chart->add_series($expenses);
$chart->set_labels($labels);
echo $OUTPUT->render($chart);

Example:

bar chart.png

You might want change how your bar chart are displayed:

Stacked Bar

To display stacked bars, you can call set_stacked() method, setting the parameter to true.

$chart = new core\chart_bar();
$chart->set_stacked(true);
$chart->add_series($sales);
$chart->add_series($expenses);
$chart->set_labels($labels);
echo $OUTPUT->render($chart);

Example:

stacked bar chart.png

Horizontal Bar

To display you bar chart in the horizontal position, you need to call set_horizontal():

$chart = new core\chart_bar();
$chart->set_horizontal(true); // Calling set_horizontal() passing true as parameter will display horizontal bar charts.
$chart->add_series($sales);
$chart->add_series($expenses);
$chart->set_labels($labels);
echo $OUTPUT->render($chart);

Example:

horizontal bar chart.png

Line

To create a new line chart, just create an instance of chart_line class. By default, lines are tensioned.

$chart = new \core\chart_line();
$chart->add_series($sales);
$chart->add_series($expenses);
$chart->set_labels($labels);
echo $OUTPUT->render($chart);

Example:

line chart.png

Smooth lines

You might want to change you line chart to display smooth lines:

$chart = new \core\chart_line();
$chart->set_smooth(true); // Calling set_smooth() passing true as parameter, will display smooth lines.
$chart->add_series($sales);
$chart->add_series($expenses);
$chart->set_labels($labels);
echo $OUTPUT->render($chart);

Example:

smooth line chart.png

Pie

To create a pie chart you just need to create a new instance of chart_pie class.

$chart = new \core\chart_pie();
$chart->add_series($sales); // On pie charts we just need to set one series.
$chart->set_labels($labels);
echo $OUTPUT->render($chart);

Example:

pie chart.png

Doughnut

You might want to change you pie chart to be displayed as doughnut:

$chart = new \core\chart_pie();
$chart->set_doughnut(true); // Calling set_doughnut(true) we display the chart as a doughnut.
$chart->add_series($sales);
$chart->set_labels($labels);
echo $OUTPUT->render($chart);

Example:

doughnut pie chart.png

Series

Series can be defined as a set of values. To set series of a chart, you need to create an instance of chart_series object and pass the title and an array of values. The title and the data are displayed when mouse over the specific point representing the serie on the chart. The number of values of the series must be equal to the number of labels.

$serie1 = new core\chart_series('My series title', [400, 460, 1120, 540]);

Properties

Title

It is possible to set a chart title, by calling set_title and passing the title as string method.

$chart->set_title('chart with a title');

Labels

Labels are the description in which the data will be grouped, in the example above labels are an array of years. The number of values on the series must match the number of labels.

$chart->set_labels(['2004', '2005', '2006', '2007']);

Axis

You can customise chart axis (X,Y) by setting title, position and change the step size. Firstly, you need to select the axis by the side you want and providing the index and whether you want to create the axis if it does not exists.

$chart = new chart_line();
$xaxis = $chart->get_xaxis(0, true) // Select the index 0 of X axis and pass true to create the axis if not exists.
$yaxis = $chart->get_yaxis(0, true) // Select the index 0 of Y axis and pass true to create the axis if not exists.

Once you get the axis you want change, you can change the attributes you need. It is also possible to select multiple axis, for example if you want to have custom steps labels in one side and data in the other.

$chart = new chart_line();
$xaxis1 = $chart->get_xaxis(0, true) // Select the index 0 of X axis and pass true to create the axis if not exists.
$yaxis1 = $chart->get_yaxis(0, true) // Will display the default axis steps information.
$yaxis2 = $chart->get_yaxis(1, true) // Select the second Y axis.
$yaxis2->set_position(chart_axis::POS_RIGHT);  // Now I can change positioning, labels and etc just on the right side.

Axis title

Axis titles can be displayed on the chart sides and can be used to provide additional information about the chart.

$chart = new chart_line();
$chart->get_xaxis(0, true)->set_label("I'm the label for X"); 
$chart->get_yaxis(0, true)->set_label("I'm the label for Y");

Axis position

You can define the position of axis by calling set_position() and passing the axis position constant (POS_RIGHT, POS_LEFT, POS_BOTTOM, POS_TOP).

$chart = new chart_line();
 
// Customise X axis.
$xaxis = new chart_axis();
$xaxis->set_label("I'm X, but at the top");
$xaxis->set_position(chart_axis::POS_TOP); // You can use POS_BOTTOM or POS_TOP for X axis, in this case let's change the position to the top.
$chart->set_xaxis($xaxis);
 
// Customise Y axis.
$yaxis = new chart_axis();
$yaxis->set_position(chart_axis::POS_RIGHT);  // You can use POS_LEFT or POS_RIGHT for Y axis, in this case let's change the position to the right side.
$chart->set_yaxis($yaxis);

Step size

Step size can be described as the size between the axis labels. You can set the step size of the axis, by calling set_stepsize() and passing the step size number.

$chart = new chart_line();
 
// Customise X axis.
$xaxis = new chart_axis();
$axis->set_stepsize(5); // Chart steps will be displayed as  5, 10, 15, 20...

Step labels

If you prefer to display custom labels instead of numbers, just get the axis and call set_labels passing an array of labels:

$chart = new chart_line();
$chart->get_xaxis(0, true);
$chart->get_xaxis(1, true)->set_labels(['Poor', 'Average', 'Good', 'Perfect']);

Min and Max

You can customise the minimum and the maximum value of a axis step size.

$chart = new chart_line();
$xaxis = $chart->get_xaxis(1, true);
$xaxis->set_min(1);
$xaxis->set_max(100);

Mixed chart types

It is possible to combine two types of chart by setting the type of the series differently of the chart type. For example, to create a chart that combine a bar chart with a line chart:

$chart = new \core\chart_bar(); // Create a bar chart instance.
$series1 = new \core\chart_series('Series 1 (Bar)', [1000, 1170, 660, 1030]);
$series2 = new \core\chart_series('Series 2 (Line)', [400, 460, 1120, 540]);
$series2->set_type(\core\chart_series::TYPE_LINE); // Set the series type to line chart.
$chart->add_series($series2);
$chart->add_series($series1);
$chart->set_labels(['2004', '2005', '2006', '2007']);

Please note the order you call add_series change the order series are displayed on the chart. In the example above, the first to be displayed will be line chart and in the background the bar chart.

Example:

bar line chart.png

Renderering

All charts are rendered by render_chart() located on outputrenderers.php, once the chart object is ready, it must be passed to render() or render_chart().

echo $OUTPUT->render($chart);

Show chart data table

To make the chart data accessible to users with special needs, a link on the bottom of the chart will display a table containing all data. In some cases, the same information is displayed on the page and might not be necessary display chart table. In that case, you need to pass false as the second parameter when calling the render_chart:

echo $OUTPUT->render_chart($chart, false);

Overriding chart colours

It is possible to override the default set of colours used on charts, you just need to the following setting to config.php and set an array of hex css colours:

$CFG->chart_colorset = ['#001f3f', '#01ff70', '#F012BE', '#85144b', '#B10DC9'];